I would've made a custom battle system, because I have the know-how and I... well... know everything that needs to be done to create it in a simplistic fashion that would also allow me to distribute it with a small read-me so other projects could make use of what I created and no one has to continually reinvent the wheel but I didn't feel like it because I have a terrible case of laziness. But if I ever decide to make a 2, and I have the plans for one, it'll feature just that.
I can imagine all of the possibilities! And, hopefully, there would be those inventive users who would not just use the vanilla system, but instead make it truly something of their own by building off of it.
Drat it all, this makes me want to make it. But eh.