Interesting ideas.. But why?

It's probably too far into the game's life to re-work it from the ground up in such a way. If you make it so every deals the same amount of damage, it's only going to increase the amount of damage required to finish a fight, which means everyone is back in the same boat trying to optimize gear, rotations, stance dancing, etc to push as much damage as possible...It's just a different side of the same coin. Classic front/back row wouldn't work the way the game is currently designed, too much moving around for mechanics and stuff, you'd have to simply say ranged take half the damage and "imagine" they are on a back row. You'd also have to learn how to optimize 2 roles within your job, probably easier for some than others, but if you've only been a tank up to now, you'll have to learn how to dps. If you've only been a dps, now you'll have to learn to tank.. Same with healers and ranged, if you've never done the other job before you'd have to learn.

It does open it up for some new and interesting mechanics based on role swaps during combat, but other than that, yes you're basically talking about a whole new game. It would probably be easier to start a fresh concept than re-work this entire game for your suggestions. Not that they're bad, it would just be a lot to implement for the dev team and require a huge adjustment by the player base. So why change? You should try to justify why SE would want to spend millions of dollars to rebuild the game, and why millions of players would want to get used to a new style of playing, other than because you, personally, don't like the design.