I've had the four of them in mind as the final 4 for a few weeks now. I thought I was just going crazy until I saw this, so perhaps I'm onto something after all.
I could easily see Derrick/Cody turning on Frankie/Zach (that is assuming Frankie doesn't turn on Zach first, in which case it would be Derrick/Cody against Frankie/whoever Frankie can align with, maybe Caleb if he doesn't completely lose his mind Thursday and in the following days), with Jocasta/Victoria doing little, mainly just casting votes with whoever sways them the best. I think in which case, Jocasta would vote alongside Donny, giving the suggested alliance essentially 5 votes (Donny, Hayden, Christine, Nicole, and Jocasta).
It would be brilliant for those 4, because even if the rest of the house banded together (which I see as unlikely once Derrick and Frankie aren't working together, which both - especially Derrick - have already been planning, to some extent), they would also only have 5 votes vs. the 5 votes of this new alliance. If one of the new alliance (or Jocasta) won HOH, they could simply put up 2 of the other 5, and the votes would be 4-3 for whoever the new alliance wanted out. They would be pretty set, especially if they kept the alliance secret for as long as possible.
Unfortunately, I am likely giving them far too much credit, and this alliance will be nothing more than a whispered possibility.