If you want to switch mains for raiding Tomb of Sargeras (June 20th), this is a good time to switch.
We will be starting on HEROIC, so your new main, if you decide to switch, should be at about iLvl 900 or higher, and should be close to, but preferably have, Concordance. What we'll be looking for is DPS around the 700k range. If you think your #newmain can pull that off, please use this time to switch.
It should be said too: If you're a tank or healer and want to switch roles, this is a good time. We want to remind everybody that you should, first and foremost, be having FUN. If you're bored in your role, talk to me. We'll make it work.