According to the Elitist Jerks [Paladin] WotLK talent trees/abilities discussion thread, Seal of Righteousness is getting a decent buff come the expansion.
SoR currently scales with 26 percent of spell damage for a 2.6 speed weapon (soon to be spell power) and is the default Protection Paladin seal. According to some sources, the new SoR still scales with 26 percent of spell power, but also gains an additional 14 percent of the Paladin's attack power. This is an unequivocal buff, though it's possible that this is a trade off for the loss of Judgement of the Crusader, as well as a push for Protection Paladins to have some Strength.
Because strength/attack power will be the threat stat of choice for Protection Warriors and Tanking Death Knights, I'm assuming that a decent chunk of tanking gear will have both the traditional tanking stats and a little strength. Take the Eternium Greathelm as a prime example of what I see coming. Under today's gearing regime, This helm is still useful for Protection Paladins, but only for the stamina, defense, and sockets. The strength is all but useless for Protection Paladins and they may as well pretend that it's not there for all the good it does them.
Under the WotLK gearing regime, strength will become a secondary threat stat, just behind spell power, which Protection Paladins will be getting from their stamina via Touched by the Light. Paladin tanking gear, thus, can be identical to Warrior and Death Knight (minus the shield) tanking gear since their spell power comes from talents. The strength the Warriors and Death Knights love will help buff Seal of Righteousness, Hammer of the Righteous (based on weapon damage and thus improved by strength), and Shield of Righteousness (based on block value which is improved by strength). On a side note, some sources have said the strength will be buffed to increase block value more than it is currently, making strength a minor mitigation stat as well.
I hope that I'm not boring everyone with this theory, but I have a great interest in theorycrafting for ideal gearing and talenting (but I hate the math). And to Honor's Hammer, I hope you enjoyed this post, and good luck if you decide to go Ret.
For the Horde and the Naaru!
Edit: Elitist Jerks pins the SoR damage per swing at:
Damage = 0.05 * WS * AP + 0.1 * WS * SP
WS = Weapon Speed
AP = Attack Power
SP = Spell Power
Some reports are coming out that Seal of Vengeance and Seal of Corruption are also scaling with both attack power and spell power, reinforcing the roll that strength will take as a threat stat for Protection Paladins.
Edit 2: Early experimentation with SoV/SoC has led to this formula (proc is the holy damage you deal per swing if a full stack is already present):
DoT: Damage = 7% * AP + 3.4% * V * SP => 7% * AP + 17% * SP @ full stack
Proc: Damage = 2% * SP