Casuals that can fight in RSS will be able to profitably get to 75 and grind xp at that level. It does not mean this is desirable because at level 75 xp for level 70 and below mobs will suffer the 5 level drop xp penalty. So only get to level 75 if you can consistently handle level 70+ mobs because otherwise you are stuck basically grinding out SLOW xp in places like MPG where the mobs xp will be halved. Presumably there will be new spells but I am not sure what else the dev team can really add to the shaman line up of spells. Our main spell set is rock solid as it is, and I am not sure what can be added that would be much different than what we got. The past spell developers already created a set of spells that covers pretty much anything we would want to do and does it well.
When my group fights in RSS my shaman is strong and powerful, and a huge asset to our group. My chanter is far less versatile and is basically a fragile slower and nuker. Crowd control is a matter of someone off-tanking adds, where my shaman comes into glory by being able to help out with heals when needed while all my chanter can do is slow and nuke. My shaman is much much more durable than my chanter so when I get aggro (which don't happen often I work hard to not get it), my shaman will usually survive - well actually usually has been 100 percent - while my chanter will just wait a little longer to attempt slowing and debuffing due to the risks involved.
Because the previous spell developers made shamans so strong I can't imagine what new stuff could be added to improve shaman abilities. On the other hand my chanter gets more and more useless as the content ramps up. Crowd control in any challenging content is someone off tanking, then the off-tanker gets rock solid aggro before stopping attacking, and ony then do I attempt to tash and mezz. Maybe I am playing my chanter poorly but it sure beats tash mezz resist die. Furthermore, if the new level 71-80 mobs have even more dps and higher MR resists than current content does, I can't imagine ever having my chanter touch a mob before someone locks down aggro on it.
For my shaman the future is bright. I can see level 75 with new buffs (for level 66+ toons probably), a stronger version of crippling spasm, and more powerful heals. More efficient heals and maybe a better canni would allow more shaman to be able to fill both the slower and main healer roles simultaneously in RSS and higher groups. For my chanter I can see lots of MGB C3s in POK at the main bank

I find it interesting that if I am 2 boxing my shaman and chanter and need to do crowd control on a single extra add, I go to my shaman and try VP with its -30MR resist to root park rather than to my chanter with mezz. CC is just safer and more reliable with my shaman.