While I do think there could be some kind of middle ground where we can use Naggaroth as contrast with Ulthuan in negotiations, I really think we should think long and hard before actually pushing for it.
We could point out that Marienburg has, with Ulthuan's support, left the Empire mostly without coastlines or the power to travel via sea or project naval power effectively. And by extension, this means that the Druchii are not that huge a threat compared to every other non-Dwarven polity in the world.
We could hope that they are smart enough to realize there are some unwise individuals in the Empire (which aren't us) who may in fact consider negotiating with Naggaroth due to this, and that they may start taking steps to ingratiate themselves a bit more with the Empire to prevent this.
Unspoken is the fact that Naggaroth diplomats are
right there in Laurelorn.
When your suggestion has an "or else" built into it, it is extortion.
I do think I'd prefer to leave it as an unspoken implication, but 'extortion' is a huge stretch. If Ulthuan won't come to the table, then unless we decide to go for less ideal leyline options, we would
probably have to look to Naggaroth for the leyline keyphrases. That would just be what happens.
It's exactly the same thing Queen Marisith of Laurelorn is doing right now. She's literally playing the two factions against each other whilst dancing around the idea of committing to who is the real Phoenix King.
So either she's a blithering idiot who's childish attempts at politics is going to result in the complete extinction of her people, or maybe, just maybe, playing the two sides against each other is a valid form of diplomacy.
There is admittedly also the middle ground to consider, which is that what she's doing is risky but doable because of Laurelorn's unique status as a super isolationist elven polity that has only recently stuck its head out of its shell. And by simple fact of being elves, they will already be seen by Ulthuan and Naggaroth as equals to negotiate with, not dumb primitives that have recently been given fire by Teclis and which can either be safely ignored, be condescending to, or taken advantage of.
Also important to consider is that Marrisith's job as queen essentially means that she has a tremendous amount of experience herding elves and handling politics. She is far more skilled at this than we are ever likely going to be.
