I guess I have to understand better why this is a Thing. I mean, I've known Scratchers to go through three usernames in a year, but people just get confused, I think.
I just have trouble seeing this ever get to the top of the list of needed features, rather than that we're against it in principle.
About deleted accounts, I don't think we should let the name be available quickly. Maybe, you know, seven years later, like when you get to throw out your old tax return papers (in the US anyway). Otherwise there's too much likelihood of someone getting in trouble about someone else's actions, etc.