This could be good, but for players who Don't want to be known as previous aliases this would not be good. If it happens I think their should be a way to toggle it off/on.
I don't think this is a good idea, for the simple reason that most players had a very good reasons to change their name. And I'm not too sure how many would appreciate it to be confronted with their old name again. Just to explain myself I'm going to use an extreme example here... Say someone used a name which they really, really, disliked but they kept using it because they didn't want to spend money on getting an alternative account (or they couldn't). Now; name changes are finally here and soon they'll finally be rid of that nasty name once and for all. Soon enough everyone will have forgotten all about $silly_name and will be using $normal_name. But if you bring those two together then it becomes quite possible that people will continue to use both to address players. Some won't mind, but what about those who do? If people changed their name then I think they did so for a reason, so I'm not too comfortable with the idea of continuing to remind them about their old name. Another problem here is that /p already supports tab completion. And not just that; it supports that for the entire server. Try it: /p ai <tab> (where 'tab' means "press the tab key"). If you add the old names into this mix as well then I can't help wonder if it wouldn't become a bit too much. (I realize that your main focus here is on displaying the names in the /p output and not so much search on them, but I also think it would be a matter of time before someone would request that feature, but that's just speculation on my part).
I agree with sheluser on some points - it could cause confusion if someone gets called by both their old name and new name, but I think would be good for just a little while, until the novelty of name changes has worn off. (maybe /p show the old name for a few weeks or a month, but after that, it doesn't show?)
