Good idea and I've been talking about this type of game for a while now. I like the idea of limited abilities per class. Classes are more like things you collect that permanent.
Here are variations that I would implement on your idea.
1. Instead of separate characters like MOBAs, you collect classes that you can stick together to form different combinations. Think of it as crafting your own Path of Exiles ability "cloud". I hate alts personally, so my bias is in promoting a single character rather than having access to dozens.
2. Your "end game only" world is spot on and I can't believe devs continue to make games that promote longevity but put in millions in development time creating content that has a very short lifetime for each character. They design in obsolescence to content that is abused in every single game then trashed.
3. Instead of using currency to get gear, I would most likely create either a Diablo 2 like loot system or create static drops like EQ that you can go after.
4. I would get rid of all the currencies and instead create character progression gear/talent points/skill points/whatever based on Achievements. Also completing achievements also unlocks other areas in the game. No more experience, the game is based off of what you can finish in the game.