As for types I would want the gymsto be this generation (in no particular order)
I would like Bug (confirmed)
Rock (a strong rock type gym for once would be cool)
Dark (needs and deserves a gym)
Fairy (New type, new gym)
Fire (Only have two and last one was Flannery, soon to be 3 generations ago)
Grass (Only have 2, and make this one a guy this time!)
Psychic (Last had one 3 gens ago too, and I am tired of psychic as an Elite 4 type)
Ghost (I like ghost types, and I would rather have a third ghost gym than another Elite 4 ghost trainer)
Although I expect to see fighting based on what the leaker said, I just would rather not. And seeing Clemont's design, I expect him to be Steel or Electric. I would rather him be steel though. Too many electric gyms! Also, no more water gyms please! Also I want the final gym to be a different type. So far they have been ground, dragon, water, electric, and then dragon and water again. Do a new type for final gym. Something difficult and not done before.
As for Elite 4, I would like them to be something like this. Types that we don't see used much and types that can provide some challenge or something different.
Poison (my personal favourite type)
Steel (It's a super defensive type, could make for a strong elite 4 member.)
Flying or Dragon maybe (dragon is done a lot, but hey, we can toss it in just because it's cool)
Electric
Champion would use multiple types. I prefer Champions like Blue or Cynthia (my favourite champion) to ones like Iris and Wallace. One that uses just one type just doesn't feel as difficult and they just seem like another leader along the way. They don't feel like the champion that took everyone else down.