Total speculation here, but the announcement of Deathwatch getting a new codex included this statement:
The Deathwatch are being reinforced with some exciting new content including mixed units of Primaris Space Marines and specific Stratagems
This let me to wonder whether new codex will have two Troops choices: Kill Team and Primaris Kill Team, or if it will have a single Kill Team entry that lets you mix-and-match Primaris and non-Primaris units together.
From a fluff perspective, given Bobby G's decree of "Thou shalt accept these Primaris marines, and thou shalt fight alongside them," from a fluff perspective I really want it to be the latter option. Being able to drop a Reiver or Aggressor into a Kill Team along with a Biker and a Terminator just sounds fun. Also, having that many options and special rules in a single unit would definitely secure the Kill Team as the single most complex unit to build in all of 40k.
But the way the Primaris marines have been pretty heavily segregated in the rules so far, plus the wording of "mixed units of Primaris Space Marines" makes me think they'll continue to be separated, and we'll have the amazingly-customizable Kill Team as it exists now, and a Primaris Kill Team which will only have access to Intercessors, Aggressors, Hellblasters, Inceptors, and maybe Reivers (though with Scouts being absent from the standard Kill Team options I wouldn't be surprised if Reivers were also axed).
So what does everyone else think? Are you hoping for a smorgasboard Kill Team that can field everything from the Primaris and non-Primaris options together in a single unit, or would you prefer having the Primaris Kill Team be its own separate thing?