Guild Wars 2

A booster item that, when active, upscales characters to max level in PvE maps, like they are in WvW. This’d only last for an hour or so, and after that would persist until map change so players don’t suddenly find themselves in an area surrounded by enemies that have 50 levels on them. (There might be some issues with rewards that aren’t designed to scale down, and with the map reward system coming in HoT.)

Two target audiences: friends of existing players, so they can explore places like Orr, the Silverwastes and the Maguuma Jungle together, and alts of established players, so they can do things like guild events. They won’t be able to entirely subvert the levelling process (can’t get masteries, will be weaker thanks to scaling, it runs out after an hour), but it’ll let new and old players play together across most of the game instead of just in the starting zones.

iirc they actually had a leveling up feature during game developement, I think you had to be partied up with a higher level character. They took it out before the beta weekends so I guess it didn’t work out. Perhaps they didn’t want new accounts to skip the low level areas where they were supposed to be learning how to play and go to higher level maps.

Even though it has the drawbacks you’ve listed, the name is too good for this to not be implemented.