I still have a bunch of ideas running through my head that I never actually got a chance to write down. So I may as well put some down now. (Plus no WoW is slightly boring. :) )
I mentioned in a comment that paladins were very close to being fixed, in my view. These are the basic, essential changes that I would make.
1. Remove the Flash of Light spell.
Reason: Flash of Light is the real problem with the paladin class. A single cast of FoL heals for a trivial amount, but at a trivial cost. This means that a paladin generally casts multiple FoLs in quick succession to actually do anything. I've heard Flash of Light described as a "channelled heal-over-time spell." And this is precisely what it is. The paladin stands there and channels her mana into the tank's health bar.
The problem is that if you are channelling, you cannot do anything else. And the essence of a paladin is doing multiple things at once! The mechanics of Flash of Light cut across the very grain of paladin playstyle. So remove Flash of Light in its entirety. Soloing will not miss it. PvP will not miss it. And PvE will be better for its absence.
2. Change Seal of Light to heal all party members when it procs.
Reason: The paladin is a support character and needs to help heal her party. This ensures that while the paladin is attacking and cleansing, her party is getting a small heal. A heal-over-time in essence, one that requires the paladin to attack, but forsakes any extra damage the paladin can do. This mechanic is much more in line with the feel of a paladin.
3. Reduce the effect of +heal on lower ranks of spells.
Reason: See this post. As well, makes spamming Holy Light (Rank 4) a less useful tactic, especially with the new Seal of Light.
I think these changes are all that is necessary to push the paladin to a front-line role, one more in line with the vision. They are not overpowered changes. Indeed, the paladin is arguably worse off than before, in terms of raw power. "We had to nerf the paladins to save them," as it were. :)
(I would probably consider adding a small +heal coefficient of ~10% to Seal of Light to compensate.)