Yes. Very possible. I am doing this now for a very large client (known for their memory cards haha).
Lots of others doing it too. In fact, much like when there was not a FPM option (or more truthfully, there was not an non-Adobe option), many 3rd party companies developed solution to help you build WDA forms for HCM P&F. Now, I am seeing the same for UI5. In fact, one 3rd party came out with a "product" a short while ago ("product" in the sense that it is more likely an "accelerator" for UI5 that helps get their foot in the door for consulting but that is pretty typical for such a complex solution), and from what I saw (little), it looked good. I think the company is called "HighStreet" or something like that (can not look up at the moment).
In any event, yes, it is very possible...just THINK through the architecture, and it should make sense. You will have your work cut our creating quite a few custom OData services though....so be warned! 