Yes, if you cast heals or shields you probably can sustain your TP, but does it make sense to balance the job assuming you'll be assisting in healing? Not really. The potency lost in SwO is so great that it'll almost always be better for the healers to pick up the slack and they'll always tune the content for 2 healers' output, not 2+1. As MT casts will still cancel...Paladin's healing will always be an emergency thing, not part of the core rotation so TP consumption must be balanced without factoring it in.

As for a DoT, I was thinking along the lines of recycling an old animation and making it PLD's version of Scourge. 500 potency of light or wind damage that costs MP to use. Alternatively, the MP could be blown on a big AoE skill, but I personally think that if PLD ever does get an AoE it might be better for it to be TP-based to encourage Flash use.