I did see this late last night, Sydney time, but I felt it better to take the time to consider each step you’ve taken in some detail. If I repeat anything that we’ve already discussed here, it’s to inform the wider community who wouldn’t have been aware of what’s going on.
Languages: I admit I had to look up Pali – which Wikipedia tells me is the liturgical language of Theravada Buddhism – but its use in context here makes sense. I’m guessing that you intend *Hindi to be the language of the average man and keeping the others as used by the educated classes? Possibly Serovitic is as dead on Arden as Sanskrit is to us.
Ethnic composition: I don’t think I have enough context to comment on this beyond a guess that these are essentially tribal distinctions, if Sartanji is their common parlance. Some points of differentiation would be useful if you proceed further, for reasons I’ll come back to later.
Overview: The piece on the Sabhian Unity claims that the Unity was forgotten to such an extent that even the people who lived in its former capital didn’t know about it by the 1920s – so it’d be perhaps unlikely that the Vishuri would remember it any better; they may themselves think that they emerged fully formed like Athena from the brow of Zeus, and are only just learning the greater depth of their history (with the help of Messenian historiography). It’s maybe a bit presumptuous for Mahavishuri to claim succession from the Unity in any more than a cultural sense anyway – the heart of the Unity was in southern #117 – but I’d hope you can demonstrate how this works later. How much it constitutes a regional power goes back to the “tribal” split and how far this is sublimated in the interests of wider unity, although if it is the kind of trading centre you’ve envisaged, this might help it punch above its weight.
History: The end of the Unity was something I deliberately left open, but as stands it’s in the late 15th century, about 200 years before your proposed date (with Messenian traders expanding into the vacuum caused by its collapse), so you’d need to push the date back or fill in that gap somehow. We did talk about the idea of Bhramavadic monastics (which seemed natural enough given Bhramavada’s more contemplative nature). The “island-hopping” towards the south-eastern peninsula was referred to as being done tentatively under the Sabhians – presumably better shipbuilding techniques made this easier? The reference to trade in the late 18th “mainly in Voraey”, I’d guess, is an expansion of trade that would have been happening on a low level since Voraey was established (1462?).
The Messenian influence on Mahavishuri in the mid to late 19th C sounds similar to, say, Egypt under Mohammed Ali, which doesn’t seem infeasible to me. Sirian presence would bring missionaries without doubt; Cairans perhaps also (Arlaturi do not, and I’m glad you left them out here). But although I can see you want to play up antipathy with Yfirland – which I’ll return to – I’m not sure it flies as a reason for the intransigence in the 1900s; just the weight of influence of Messenian commercial “exploitation” is more than enough, surely.
Leaving aside Mahavishuri’s involvement in the Long War, the establishment of the Council of Truth makes sense – if there is a particularly weak monarch. If so, then the Council should surely not yield power back to the monarchy without a fight – potentially even leading to civil war. I know you’re keen on an “Asian” feel to the place, and recent developments in Thailand suggest themselves here.
Government structure: I’m not sure what you mean by a caste structure here, unless these three groups have superiority to the general masses. You do actually contradict yourself in that if “the sacaraja has total power over the whole kingdom”, then the dattva cannot be “granted full autonomy from the sacaraja’s rule” – although there’s arguably nothing to prevent a wily dattva, or the mantthan collectively, manipulating a weak sacaraja in best “power behind the throne” fashion. The reference to the dattvas having “the right to bring destruction on other dattvas”, even if the sacaraja must be in accord, does suggest that they are functionally kings in their own domain, with rights of high justice – again, inconsistent with an autocratic central ruler, I’d think.
Politics: “The Dāttvas and Sacarāja see each and every one of them as pawns to each other to be played” actually makes them much closer in spirit to the Yfirlanders than they probably admit. This kind of backstage jockeying for position does probably make for decidedly weak government and opens all sorts of opportunities for devious outlanders! But the reference to the Sacaraja’s “ability to massacre and/or destroy the Dattvas” is confusing if the Dattvas have the power to control him in some circumstances. Again, you either have an autocratic monarchy or you do not; it isn’t really a mix-and-match arrangement. What I think you’re saying is that the Sacaraja is supreme monarch with the Dattvas playing their internal political games to gain influence at court or divert the Sacaraja’s displeasure elsewhere when things go awry – please tell me if I’ve misunderstood.
Foreign relations: I can see why the Mahavishuri would have a hate on for Yfirland, but I suspect it’s a bit overdone as it stands. The base premise of Yfirland is a kind of cross between apartheid-era South Africa and an organised crime syndicate – certainly the hate wouldn’t be reciprocated; Yfirlanders would probably just hold Mahavishuri in contempt just like other “nonnar”. Arguably the relationship may be closer to, say, Rhodesia against the likes of Mozambique or Zambia in the apartheid era. (The Yfirland army would almost certainly have a hand in any internal conflicts in the region. I described them as “state-sponsored mercenaries” for just that reason. And if you want a hate figure, then Viljafost Lysu offers a much better and more recent target.) Certainly, they would be aware that Siurskeyti regards Yfirland with more distaste than almost anyone else (as a “perversion” of Arlaturi mores).
Would the Vishuri be astute enough to make a distinction between Orthodox Cairan Odann and Reform Cairan Savam? I’d doubt it – more likely that the Odannaigh have commercial reasons for being a problem there (as well as their looming presence on Diothun, which isn’t all that far away). I would presume also that you have something in mind to explain the recent good relations between the Vishuri and #120. And Mahavishuri may try to ignore the Ascesian Banner or pretend that it does not exist – but I suspect that the reverse is not true.
Cultural overview: I do feel that this is too optimistic a picture, particularly when combined with the multiplicity of ethnic groups which you mention elsewhere. Oh, I don’t deny that this is probably the impression that the Mahavishuri rulers want to present to the outside world, but – whether by accident or design – what you have seems very similar to the ut possideatur principle elsewhere in the continent where diverse groups are controlled (sometimes tenuously) by an overarching government. I’d expect to see some greater tensions here in practice. I do very much support the prominence of art in Vishuri culture as an expression of Bhramavada, and I agree that the faith lends itself to an expression of monasticism. (It also could support warlordism, of course – I referred to the “Mahish heresy” as a nod to Maugissism in the “old” Isealism – and that could be intriguing as well.)
All told, I think it hangs together a bit better than previously, although your logic is a bit weak in places and you may want to think through how the structures you’ve set up would work in practice. Doing so may actually help you build some of the country’s more detailed history, so it’s a worthwhile exercise in its own right as well as making Mahavishuri more believable as a concept, which is the name of the game here. Persevere!