If I understand what you are wanting (which I understand that I may not due to a language barrier, and that is okay), this idea is not really that new at all.
The way I am understanding your post is that you are wanting to pick your champion model, then either pick from an assortment of abilities from other champions, or to simply use the entire kit of a different champion instead of the kit of the champion model selected.
In either case, it would just be confusion for the sake of confusion.
It may make some sense for similar champions such as the ones you listed.
If Ashe were to fire Mystic Shot from her bow, it might look strange and throw your enemy off for a second, but it could be plausible.
However, If Ashe were to run up to you and start using Broken Wings (Riven's Q), and bashes her opponent with her bow, it would look really funny, but it would be really dumb.
If you are referring to using a grab-bag assortment of abilities, there would be many abilities that would simply be off of the table.
For example, all of Azir's abilities aside from his ultimate rely completely on his W ability, Arise. No Sand Soldiers, means you can't use Shifting Sands (Azir's Q) to move his soldiers. That means you would need to use at least 2 of your "ability slots" in order to use anything from his kit.
A champion's kit is balanced completely around their resources, cooldowns, and other abilities available to them. If you were to take a champion with a low mana pool and give them a kit from a champion who needs a high mana pool, that champion will have a very difficult time.
So in conclusion, .. I'm going to have to say that this is really just a bad idea that would simply not work.
The closest thing I think you could get to seeing something even remotely in the area of this would be The Doom Bots of Doom. And the ONLY reason that works is because the bots are A.I. controlled.
