I'm not really worried. Personally I see this a couple ways:

1) Theres no way shamans will be nerfed so bad they're unplayable while multiboxing - seriously, this just won't happen, it never has happened to ANY class regardless of what anyone says, sure some classes get nerfed to where they're "less effect" but not so bad that everyone just stops playing them. If they are nerfed so bad its hard to level they will be buffed, this is how blizzard has always done it and anyone who says otherwise is a conspiracy theorist or an overreactor/exaggerator

2) RAF means leveling a second team is easy. Personally I'm working on a priest + 4 locks right now, will be a great PvP team i think. Worst case is you could boost a pally to level 60 instantly and level that to 70 to be a tank for your 4 shamans which would still make them EASILY able to solo heroics.