It sounds like it would be a bit overloaded yes, and finding the seasonal icons and their like could get annoying in the midst of tons of champion related icons for veteran players.
Perhaps there's some viability to having an icon for your most played champ (either of the champ or one of its abilities) that would replace itself if your most played champ changed?
Then again, just ability/champ icons is a bit plain compared to the other options which are more unique, and there are already the teambuilder icons if you just want to show off your prefered role...