Huh, that's an interesting idea. Zero-K definitely has a bit of a learning curve, but I don't think its because of the size of the units. If you take games like Age of Empires or 0AD, the vast majority of units are people, and people have very small footprints--basically like your standard raider size in ZK, yet that doesn't seem to turn people off at all.
And, you can already do this in normal ZK. Just zoom in and you can see and control the units better. Yet, the majority of players spend most of their time doing the opposite.
Good unit design is being able to make out details of units and distinguish units from each other even when they are very small (like when you're zoomed out). I actually think Zero-K does a really good job of this compared to a lot of other games. Like, there are no two units that look even remotely similar, which is impressive given how many units there are.