I don't know about that, mixing UBW into HF could work, if done properly.
Well, the problem is that HF requires Archer and Shirou to be on the same side, whereas in UBW they have to fight each other. Plus, Saber disappears early on in HF, and Gil attacks and is eaten by Sakura (which is what sends her on her final rampage). So, I'm not sure how much of UBW would be left to fit into HF, aside from the bits that are already there (like Archer's identity and Rin's character development).
Also, Shirou's character development is somewhat different in the two routes, as is
Rin's for that matter. UBW Shirou is a lot more idealistic and optimistic about his ideal, whereas HF Shirou runs straight into the issue of "saving one vs. saving many" and decides to protect the ones he loves above all else. They're not as different as some people make out, but Shirou's idealism vs. Archer's cynicism is part of the
point of UBW, and I don't see how you could fit that into HF given what happens with Sakura.
So far it sounds like they're going to be doing all three routes, which would be fantastic. Fuck DEEN.
Yeah, although I hope (without much expectation) that they do HF first.