For this to be as awesome as it needs to be, larger the warp core, larger the explosion. A Defiant would cause 1/3 the damage of a Galaxy due to the sheer difference in the size of the ship.
But also on the topic of improving PVP in general (which can be worked with this ^^ proposal) would be the limits on deaths in PVP.. .
****Hypothetical (Don't kill me)****
While in a space arena, each player would get a certain number of "lives" (Like in a game like Pac Man) determined by the type of map or by the leader of a private match. Limits could be as low as one, making each battle be one battle and not 15 or more like our current arenas. I feel in general there should be only one life during a PVP match, excluding Cap n Hold (due to the nature of the minigame).
When a player is destroyed (or runs out of lives) they would not be given the option to respawn, in turn they would have the option to "free float" (Like in a FPS) between the remaining team members points of view and observe the rest of the PVP match, or the option to leave the map/team or both.