The idea makes so much sense that I'd like to think that Google would be for it... unless, of course, for some reason it's algorithmically not possible.
I've read in various fora that the perceived sandbox effect in a domain change was an unanticipated consequence of a bunch of other factors (eg, link crediting delay, etc), but that Google decided they actually liked the result because it was effective in combatting spam. It may be that Google can't undo all these factors with the push of a button.
I can also imagine that the evaluation of what is a legitimate name change request could get complicated, if not messy. steveb's objection is a fair one.