So with the new episode having just come out (the last mablecorn) people are obviously worked up. Lots of new info, but what stuck out most to me is that bill used to control Ford, and, most notabley, will pick a new host. Someone who does not live in the mystery shack.
Its pacifica. Here is why, when Pacifica was first introduced she was a sort of antagonist twords the twins but after the northwest mansion mystery episode she was revealed to be a bit more of a complex charachter and a potential love intrest for dipper. This will play out well if Bill controls Pacifica because after them just gaining trust it will hurt all the more if she becomes one of the worst villians on the show, and might lead to some reveal of feelings from dipper ;)
Plus i think if he controlled anyone else on the show it might be a bit silly
P.S. didnt even think about lil gideon. He is just as possible too.