Bursts aren't Ranged attacks; they're Close or Area attacks. A power that goes off in the middle of the party and hits everyone for damage will be a Close or Area power; the Warlord's ally has thus not been hit by a Melee or Ranged attack, and Tactical Shift cannot trigger.
-Hyp.
You are entirely correct... I withdraw the amplified objection; this ruling would only rarely amplify this power to multi-target protection.
However, this changing (via purposeful ignoring) of the triggering rules for OAs and OA-like Interrupts such as Combat Challenge (which is really what is being proposed here... the critical matter of the question has little to do with Tactical Shift and everything to do with OAs and the like) does allow similar response on Area powers. You could wait until the to-hit rolls are done to decide if that attack is worth responding to. An OA you almost always take when offered, but OA-like Interrupts that trigger on attacks often involve a choice, and by the rules that choice is made at the time the attack is announced, before you know if or how many it is going to actually hit.