The Trident already is a semi-independent major polity within the Empire. Three elector counts meeting on the yearly and coordinating with each other while the other provinces bordering them are not invited? Yeah. Power bloc. One that will look inward in response to exterior pressures. That's already going to do Interesting Things when Magnus the Pious finally kicks the bucket, and it's exacerbated by tensions with Middenland.
The danger with diplomacy with the Wood Elves -- which is too good a chance to pass up, mind, because it is the direction that things *must go* if the overall stage is to move in a positive direction -- is that it amounts to this quasi-independent major power bloc starting to carry out organized foreign relations independent of the empire.
It's one thing to be a power bloc. It's another thing to be a power bloc which is starting to act like it's independent; which is starting to look like it's only acknowledging the Empire as its superpolity because it feels like it. People would look at Laurelorn joining the Trident meetings as... Well. Bluntly: with Laurelorn on their side, the Trident could walk out of the Empire in response to the election of an emperor it found distasteful, and there would be very little anyone could do about it.
And this is ignoring the brewing tensions with other provinces, *and* the existing tensions between Laurelorn and non-Trident provinces.
There are circumstances in which doing exactly that -- crashing the Trident out of the Empire and allying with Laurelorn -- would be a really fucking good idea. Encouraging people to look at us like we're going to do that is a horrible idea. Inviting Laurelorn to the Trident meetings when we don't invite (and can't invite convincingly) e.g. Middenland? Everyone knows the Trident is *deeply* allied internally and that the meetings are part of that.
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That's one half of the coin.
The other half of the coin goes like this: so what?
So what if the Trident is functionally an independent bloc inside the Empire. By the nature of the quest, Ostland is always going to be aware that its best interest is to keep the southern polities of the Empire in good health. The biggest danger to that by far would come in the form of an emperor hostile in some measure to the Trident. Above all we do not want that, for reasons I am sure are obvious. But if the Trident can rise from its position as a dangerously powerful bloc possibly warranting suppression, to a bloc which cannot safely be suppressed and must instead be courted, then this is a very good thing for Ostland, the Trident, and the Empire as a whole, because Ostland will always be aware it is in its best interest that the south remain healthy.
Open ties to Laurelorn could come very, very close to pushing the Trident across that line because of many of the exact things already discussed. If the Trident also made it policy to Emperormake southerners instead of accepting the Emperorship itself, I think we'd be there.
So:
So what?