The question is: If Baldur's Gate 3 is made, how do they tie it to the Bhaalspawn story.
It doesn't matter who makes it. As long as they tie it to the Bhaalspawn story, use the same engine, and the same rules as BG2.
The only way I can see it happening is if:
You either get two options, if you claimed the throne of Bhaal, you have to defeat Mask and Cyric and whatnot. Seeing as they killed Bhaal(Or so I read at a Forgotten Realms deities site)
Or if you didn't claim the throne, you still have to defeat them because they're all threatened and stuff. Whatever.
The question simply is, How and why. Too many people are concerned with who makes it. But it should be why are they making it? And how are they going to keep the continuity from BG1 and 2? That is what is important. Whoever makes it, has to make it well, or they could ruin the entire series.