Okay so as I said in the Discord I will copy my message here to get the discussion going. I personally like the idea and effort you put into this. I don't really have the background to discuss the feasibility or the dev work required for this - it sounds complex and will probably require a significant time investment. Plus there area clearly the risks you flagged as well. The more complex this flow becomes the higher the change of error or a possible exploit.
The bigger problem I see is that someone would probably need to create a new LP protocol that's independent of any of the existing projects, since as far as I'm aware this functionality to divert part of the LP pool doesn't exist anywhere. That also raises the question: why havent existing protocols explored this hybrid setup? Could be that they haven't thought of it, or it could be that there are technical/economic reasons for not doing so.
So I think there's really two questions for this topic: 1) is this hybrid pool setup interesting in general - at least to explore the concept? (clear yes to me) and 2) is it interesting for Alchemix specifically? (yes potentially to me).