I haven't done much research, but I've seen some saying there will be times splitting into 3 groups...

So will the typical setup be 6tanks 6 heals and 12dps? That seems like a lot of tanks. I'd hate to see people having to sit out though if there's tight dps checks. If you have say 3 groups doing 8 man content, and that doesn't translate to them teaming up to do 24man's I can see some problems.

So, am I worrying about something that isn't an issue? I know in rift almost every boss required different amounts of tanks healers etc, but you could easily swap between them whenever.