Giving Paladins DI as a combat res makes a lot of sense...since it is a known ability of the class. (WC3). The previous iteration had exploits, but if a battle res is so necessary that it is the Holydins Symbiosis benefit, then the spec should get a baseline version of some sort.
The previous version worked by removing the target from combat, preventing all action and killing the Paladin. Exploitable as seen in ICC.
So - add in a "cannot be Battle Ressed for X minutes after use" proviso.
And, for the Battle Res - allow that to be cast only if the paladin is dead.
So:
Divine Intervention: Removes the target player from combat and prevents all harm for three minutes or until cancelled. The target is unable to move more than 100 yards from his current location and can take no other action. Casting this spell kills the caster and prevents his resurrection under combat conditons for three minutes.
This spell can be cast if the paladin is dead, returning a dead target to life, or imbuing a life target with the Ardent Defender buff/the ability to self ressurect and preventing the paladins resurrection under battle conditions.
EJL