Can we just combined heal and clarity already?

It wouldn't be anymore versatile. No one would use it for the Mana regen purpose, because the Heal+Movement Speed is too valuable. Take Xerath for example. He's an immobile mage who likes to poke, so he takes this theoretical Heal summoner. As he pokes, he hits some and misses some, and runs out of mana. He uses Heal to get mana and some hp back to keep poking. But he's left himself vulnerable to a gank, and he already popped Flash on an earlier one. The jungler ganks again, and he dies because he used Heal for the Mana regen and not for the escaping capabilities.

I'm not saying Clarity is a great summoner, but mixing summoners like this only adds needless complexity. More utility isn't always a good thing. Would you combine Cleanse and Ghost? Just buff Clarity instead.