This is how we start ending up with prot wanting SP again. If it scales with SP and we don't want it using SP, then it must scale better with strength, but then it might scale too well compared to DKs and warriors so it gets nerfed... next thing we know we're rolling on mage weapons again.
This is true. The line between Prot paladins going for tanking weapons and spelldamage weapons is very thin. It's easily possible for a ShR that scales with spellpower to push Protection into caster weapon land, much to the dismay of the mages.
So let's take another shot at making Shield of Righteousness something for Holy to get excited about. How about playing with Infusion of Light:
Infusion of Light
Requires Holy Shock, 35 points in Holy
Your Holy Shock critical hits reduce the cast time of your next Flash of Light by 0.75/1.5 sec or Holy Light by 0.5/1 sec, or increases the damage of your next Shield of Righteousness by 50/100% of your spellpower.
Holy gets a nice 1-2 punch with a crit Holy Shock followed by a powerful Shield of Righteousness. It's deep enough in the Holy tree that Protection and Retribution can't get access to it. Holy Shield is melee-only, so it should be okay in PvP. If you use your IoL proc on ShR, you can't use it on an instant or fast heal.
It might resurrect the Shockadins with a 37/0/34 build, but I don't really see that as a negative. A new build type would be amusing.