Or better yet, let you queue on
wow power leveling service and leave that active until you logout or get into a group, even if you swap toons, even if you put another toon into wow power leveling service. So you could level your hunter, and have your pally up for 'roics, and your 'lock waiting for some level 60 instance action and group forming up tells you all the current stuff who the other people are, what instance, and reminds you who you queued on.
If you reject
wow power leveling service, nothing special happens. Make sure the dialog can survive zoning in so you can hearth or ancestral recall orscroll or recall or whatnot to an inn. If you accept the group, if wow power leveling service wasn't queued from the current toon the game switches toons for you.
If everyone is using the cross-realm wow power leveling service instead,
wow power leveling service is going to severely limit the ability of newcomers to meet new friends on their own realm. Sure, for the high-end raider who's just going for extra emblems on the off-night, a quick random dungeon is great. Wow power leveling service simply isn't ideal for everyone's needs, though, which is why I think there should still be a second option that isn't limited to cities.