I've been working with UFE for a little under a year now, and I've been dissatisfied with certain features & aspects of the engine's code. I believe it's lacking critical features present in modern fighting games, such as a buffer system to execute moves immediately after wakeup or after "Takeoff".
I believe that having a way to input a move during a basic move and have the move file executed immediately after the basic move is complete is something that would be vital for games made in UFE to be up to modern fighting game standards. Currently, partially because of this limitation UFE seems to have, "Tiger Knee" inputs do not seem to work. (Tiger knee inputs are when you do a motion input, followed by a jump and THEN a button in order to do an air move as close to the ground as possible. nearly all good fighting games are capable of this type of input.)
In addition to that, I think the input system needs a lot of work, a big factor my playtesters have complained about frequently is the fact that in order to have motion input moves be executed, the engine requires a direction input to be held at the same time as the button. In other modern fighting games, there's a small window where after releasing the stick back to neutral a command input can still be executed.
I've gone in and made various attempts to fix these kind of issues myself, and there are definitely other issues I have with UFE that I HAVE been able to solve (but not the couple here that I have outlined), but it would really be beneficial if the engine itself was updated to fix at least these couple of issues I have with the engine.
I appreciate UFE because I would not have been able to get so far into development without it, but attempting to polish the gameplay is an absolute nightmare on the coding side.
EDIT: So I've found out that TK inputs are in fact possible, oops my bad. That said, I still think it'd be easier if we could input the last button press of the move during takeoff and still have the move come out.