I believe in Joppa's last VOD (near the end) he mentioned that rangers would be flexing into a very limited off-tank via the Beckon ability line. So Rogues flex to CC and rangers to a semi off-tank.
I was hoping Rangers would flex heal later with maybe mastery in their heal removing the cooldown and/or increasing the amount healed and maybe their regen being able to be used on others (as well as increase its heal amount). Or maybe an ability on cooldown that does those things. I know Monks are planned to flex tank and Rogues flex CC; all three will likely be expected to pull often depending on the situation and group makeup.