So removing all of them and giving us a passive buff to compensate is an easy solution (basically, a permanent invocation buff). I'm trying to think if they've ever done this before though. Normally they give flat % buffs to core spells. This proved to be a poor solution (the 13% Frostbolt buff basically made it broken on the last PTR). I don't think they want to just apply a global passive to our skills and modifying any spells damage doesn't just change it's damage; it also changes how the other spells in the rotation are weighted in comparison to it.
They've already said they are strongly against adding more utility to the classes in order to make them more competitive for raid slots, so I also don't think that is going to happen.
The changes to the tier will probably be damage spells / cooldowns. Which are hard to balance. I'm open to being wrong (and hope that I am) but past trends of balancing don't support major changes like a tier overhaul which has the potential to completely change how each spec plays mid-expansion.
I know what you want to happen, it just doesn't seem realistic based on previous trends.
My main question to you right now is: Are you ok with tier bonuses alleviating the major concerns of the specs?