IMO, most of the wishlisting has it backwards.

C:Inq will almost certainly *NOT* have Deathwatch, Grey Knights, Guard or or Sisters, because that defeats the entire point of separating Sisters from Inquisition from Grey Knights from the rest.

C:Inq will have Inquisitors, Assassins, Retinues and Stormtroopers (forgot about those earlier) - those things not directly represented by SM, GK, IG, or Sisters. Likely, it's a very narrow Codex, like Sororitas Ecclesiarchy, but that narrowness allows for deeper character.

The blended forces are handled via Allies. This allows Retinues to stand for Arbites / Gangers / PDF, whatever.

And likely future C:GK will drop the Inq elements.

But the idea of an Imperial mishmash of Inquisitor, GK, Deathwatch, Sisters, Arbites, PDF, Hive Gangers and Guardsmen no longer holds. Those who bought piecemeal will be forced to expand to full armies with full Allies.

The only question in my mind is whether Inquistition will be allowed to Ally with itself as different Ordos.