Hi! Sorry, I'm very busy these days and it means I miss messages.
Yeah it takes a lot of troubleshooting to make sure your plugins are compatible. It introduces a lot of little bugs and stuff.
As for what can be done with the battle system, the answer would probably depend on your javascript coding skill. You can do a lot with the engine provided you have the right knowledge, but otherwise it's difficult to implement custom stuff.
I am still improving it and another big update is scheduled, although I have been winding down development on Memoirs. I'm always interested in feedback though!