I myself for instance likes to use all kinds of combat styles, both melee (I'm talking about 2-handed obviously in this case), ranged and magic, and switch between them. Spells is something you do pretty fast, and often once (because you normally don't have time for more). Having to unequip all the time could be annoying. I'm not sure it will be, but it could.
It also makes sense that you can hold a two handed weapon in one hand for a second. Try yourself with something heavy, and raise your other hand at the same time. It's possible, yeah. Whether it's a spell we're using with that other hand, or if we're just raising the hand to wave at someone doesn't matter. The question is about doing something else with your other hand for a second, no matter what it is (as long as it's not a physical burden as well).
BUT, we all know Bethesda has focused on making each hand like an equipment slot. Two handed weapons take up both of these. To then allow a two handed player to suddenly use a third option (a spell) for a second would be breaking the logic of this system.
So it all comes down to what we value most. Something that's logic with Bethesda's current equipment system and more tactical, or something that is possibly less of an annoyance and that is also "realistically" (as in just using one hand for a second for a two handed weapon) possible.
All in all, in this case I would prefer something that's possibly much less of an annoyance rather than a more tactical style.