I wouldn't be against the idea of somone else becoming Spider-man. Just as long as there was the proper build up to it. Also if they kept Peter in the mentor roll after that and he was always around just not as Spider-man.
I'd be willign to accept a student of his or an offspring in time. Student would be the best version until he has a kid or two. Like I said though Peter would need to be around in the mentor roll and there would need to be an interesting way for the kid to get powers.
In fact I think it needs to happen to be honest. That's just me though. They already have a decent young cast they can play around with. Young Avengers, New X-men, and Runaways. If Marvel did this right and were willing to take the chance even if meant lower sales for a while I wouldn't mind seeing them do it.
People hate change. I think everyone can see that. Some are against the idea of someone else being Spider-man for that simple reason in the very end I feel. You can't get Peter back to how he was when he first started out. You need to let him age, deage him completely or let someone else take the mantel, even if it's just for a few years. THere is a risk yeah but you never know what will happen (the whole Ben Riely thing didn't work I feel cause how it was done with the whole clone thing which seems came off insulting to the readership).
In order for something like this to even work though Marvel can't rely on current readership. Many will be against it because Peter Parker is Spider-man and many won't evne entertain the idea. No they will have to pull in a LOT of young readers new to comics. Yet the problem is Mavel and neither DC seem to be pulling younger readers for various reasons. Same for other smaller comic companies. Price, speed and time issues are released (that attention span I feel), and avalibity. If the can fix those problems (get comics out of comic shops and back onto newsstands, food stores, etc and lower the price ) they could do the legacy thing successfully. Until then don't see it happening and there is enough blame to go around for why Spider-man/Peter needs to be "fixed".