Had a thought, so I figured I'd submit it.
Merit: Savagery
Prerequisites: Fighter Level 8, Savage, and Melee 1
You are capable of feats of strength beyond those of other martial classes. Your attacks with two-handed weapons call pierce damage as long as you are affected by Strength and Rage.
Perhaps it would be feasible if you have to apply a percentage (or all) of the damage to yourself as well? It still doesn't solve the issue of how powerful it is, but it would severely limit its use, and it seems like a pretty Savage thing to me - you're putting so much into your attacks that you wound yourself in the process.
As someone developing a game as well, something like your suggestion is just too complex for the LARP medium. Firstly, how do we police that and make sure people are generally taking the approprate backlash? And secondly, that's just more math and numbers that a player who's supposed to be "in a fit of rage" to keep track of. At the end of the day, no one will track the damage correctly or at all, and therefore the move will be too over-powered.
Esgir, i enjoy the thought of what you are suggesting (especially with my plans for a big weapon soon™), and imagine something similiar to Seer's Fate Brand.
Pierce by itself is a very strong mechanic, so we'd have to balance out auto-pierce with a strong cost or counter-mechanic (uses up power attack actions? withstand actions? Trump? Weakened after use?). Even the weakened one would probably require revising the level 12 merit (as we don't want to make a merit feel 'required' to use certain builds I imagine).
I enjoy the idea of mutual-damage, but as stated, that's one more number to add-up in the heat of combat. More math, more thinking, less swinging, sad savages.
I'm gonna brainstorm on this some and look over mechanics. I do enjoy the idea. It just feels like there should be a high cost to it (something to shift from offensive-fighter to melee glass-cannon?)
Last Note: I don't have much experience with it, but I've also noticed in playing around with the npc character builder, it seems very difficult to include "everything you want" between Crushing Blows, Power Attacks, and Withstands. Perhaps a good balance with these mechanics could be found? Savage already does get 3 pierces though. Hmm.
Afraid that's a no. Something like this has been suggested before, but even adding in Rage and Strength as requirements (they're dubious limitations, anyway, since most savages always use them at that level), it's very broken. Seer pierces have incants to slow them down and scout pierces are only ever ranged. Rapid-fire melee pierces would be way too powerful.