I guess it wouldn't hurt anything to have this feature, but if retired icons still count against the usual icon limit, I don't think I'd ever use it. I understand why they would count against the limit -- anything else would be unreasonable server load and you'd probably get people trying to game the system to upload more than their fair share of icons -- but fundamentally, if I have 50 icons on my account for FandomA and I get tired of it and move to FandomB, there's generally not going to be any space for FandomB icons unless I delete the the old ones. Archiving just really isn't an option in that case.