While liquid water would be very tough to imitate it wouldn't be too far of a stretch from vlads blood. But ya I was thinking about a multi ele mage too, similar to udyr except without different forms each ability grants him a constant passive effect and each one has an active cast with 5 ranks(you would have to choose to take the hit on one of them for 3, which would give him the ability to fit different players styles)

Passive-When he drops below 10% health gains a temporary shield and movement speed bonus

Q: fireball: passive-each rank increases ability power by 7 or 8
active-fireballs deals damage ticks over time

W: Earth: passive-increases health by x amount
active- a wall(can't be cast through or moved through) would be an interesting spell similar to anivia but would require a lot of skill to use effectively, maybe the first 4 levels just do a damage reduction in 20% increments

E: Water: passive- increasing cdr 3/6/9/12/15
active- moving tsunami wave(kinda like ez's ult in terms of size) pushes back enemies it passes through and causes thick mud which slows enemies

R: electricity: passive-increasing spell vamp
active- effect similar to ionic spark hits 4 targets

They haven't made this kind of champion simply because they haven't gotten to it. If a designer wants to make this champ archetype they will.

the thing about Riot's champion design is that the character has to be unique

part of the reason why Omen was scrapped was that the designers felt he didnt look like a ranged carry, and looked like a generic monster. at least Volibear is armored and Skarner is made of crystals, Omen was just a generic monster

if there is a way they can make a elemental mage without it being too generic im sure they would do it.

Why not a champion that uses Three basic elements, Such as water, Fire, And earth. Or Air, Fire, And earth? (I see a lot about how water is hard to make), And then when you use his/her Ult, It changes all the abilities into the advance version of these elements? Water becomes an ice ability, fire becomes magma/lava, And earth becomes metal (Would kinda be based off of avatar) Or something like that?

Make it so that the skills can be combination'd to provide extra boons.