I may be wrong, as it’s been a while since I touched UDK, but are there any real problems with UDK that are ‘forcing’ you to switch? If not, stick with UDK for said product.
Are these problems not solvable without Epic’s updates? If not, stick with UDK for said product.
What I’m trying to say is, are you sure you’re being forced to switch to UE4? It’s always been my understanding that when using an evolving piece of software (in this case UDK) to create something, it’s best to start with a certain version of the product and stick with that version, unless you absolutely need that brand new feature that just came out, or that critical bugfix.
Otherwise you would end up spending more time adjusting, and porting, and reinventing the wheel, than actual development.
Just to be clear: I’m not trying to be an ****, I just seriously doubt someone is ‘forced’ to switch to UE4, as long as UDK is still available.
Another thing is, you do realise that you could probably, for example, create a Lua-binding for the engine, and do all your AI/UI scripting through that, right?
In any case, I believe that in the end, whatever you pick, pick what fits your project best, and you can’t go wrong.