I haven't played US or UM but I have played Sun and I was really looking forward to it, as it was my first Pokemon since Blue/Red and Gold/Silver (The old ones). Well I hve to say, I was a bit shocked and disappointed by Sun/Moon. While it was a solid game I got the feeling that all the new Pokemon were more or less ugly exept some. Also I can just agree that the character development etc. somehow is not that great in my eyes. They really could make much more out of it, making it a really great RPG.

As you said a reboot with a new battle system: I like the turn based one but I could imagen also a more action non turn based or half turn based one. Have you played Ni No Kuni? Something like the battle system there would maybe fit.