The selfish part of me wants to disagree but I know for a fact your vision for this game should be uncompromised. If switching engines makes the game better (especially for something like gameplay) then you should do it. It pains me that something like that could add months of dev time but no great game is created in haste. Whatever vision you have for this game should be persued to the fullest.
Some selfish requests: someone else suggested being able to change the MC's pronouns and genitalia outside of just choosing M/F which I think is a great idea. I (and most other fans I think) would also love it if you could keep us updated more. An update about what's being worked on every other week would be really nice.
Very excited for the future of this project. The beta is one of my favorite eroge I've played.