The big advantage of the AvantGrand is that it actually has real letoff. In otherwords the downweight is heavier than the upweight. When you press the key is throws some weight, but when it returns it is only the weight of the key, and not the hammer, pushing back on you. I would love it if another manufacturer figured out how to emulate this, rather than giving us the click/jitter, which is what current letoff simulations do.
I don't think this is quite correct. The real reason the downweight is greater than the upweight is that when we push down on the key, we have to overcome both the weight of the hammer, and friction. When we release, the weight of the hammer (which IS still in contact with the key, btw) assists the return, so there is only the friction. We discussed this in another thread a long time ago - there was a reference given in that thread. Anyway, if what I'm saying is correct, there's no reason why the simplified hammer actions in typical DPs could not behave the same I don't think.
Of course I agree about the let-off - standard DPs don't have a real letoff. However, the period of time the hammer is not in contact with the key is very brief - it flicks up, bounces off the strings, and then comes back down to rest on the key again.
(putting it very simply, of course!)