I don't. I forsee new combinations, new effects, maybe even new spells opening up as you level and perk up. Why is that so much different than doing it at the altar? Add in the ability to "freewheel" a bit and adapt a new spell to a new situation on the fly, instead of having to go back home to cook up a new one...
I see the new system as everything Oblivion should have had. The only thing they've done is limit the number of effects you can add at once to 2. Right?
You don't have any real control of the magnitude. That is not good.
Once again, I'll say it. Spell combinations doesn't provide the same freedom, it simply creates a single spell from 2 spells. This "on the fly" stuff doesn't have all of the creation of the altar, non of its freedom. It limits you to a single spell. What if you want more area for that spell? What if it isn't strong enough? You can't modify that any more than what they give you.