Just a quick list of ideas I have for tweaking or altering existing feats, and possible entirely new ones. What their quality would be I have no idea but I can only estimate. The numbers are just spitballed and if ever implemented would likely need to be tested extensively.
Battle-Born: The battle-born is a person born and bred for war and long-protracted engagements. Whenever a Battle-Born kills a zombie they gain +2% attack bonus (Max +160%), and +1% defense bonus (Max 80%), and they gain +20hp on kill. These bonuses are retained so long as the Battle-Born has killed or assist-killed a zombie within a special timer. The timer begins on their first kill, having 20 seconds as the maximum before losing their battle-born fury. Each kill adds 2 seconds and each successful hit with a weapon adds 1 second. If the timer reaches zero the Battle-Born loses 4% attack and 2% defense till they return to the normal values.
Replaces: Stir-Crazy & Wise
Leadership: Leadership now instead grants minor bonuses continuously to allies within 1000/hu. It increases attack damage by 20% and defense by 15% to all allies. This stacks with other bonuses (up to their normal cap), but not with other Leadership bonuses. The Leadership player gains the ability to drop supply crates like Supplier currently does, but it also gives health to the user and the Leader can use their own crates after a short delay.
Replaces: Leadership and Supplier
Valorous: Valorous grants a constant 15% defense and attack bonus to the user. Once every 30 seconds, the player may activate a heroic charge, granting them a Battallion's Backup and Kritzkrieg effect to themselves, in addition to existing bonuses. This boost lasts for 2 seconds for every zombie the player has slain since the last usage of the ability and plus 1 seconds for every assist. After this heroic charge ends the Valorous player loses their attack bonus, and their defense is debuffed by -35% (So -20% in total, before other modifiers) and their speed drops by 50. When severely outnumbered (5 to 1 ratio for zombies/survivors) the Valorous player gains continuous Minicrits for the rest of the round until death.
Juggernaut: Juggernaut once again grants it's +25% damage bonus, +50% defense bonus, and -100 speed penalty and blocks damage from self-inflicted blast damage. In addition all of their attacks contain more oomph, adding a small amount of additional knockback to all of their attacks.
Replaces: Juggernaut and Nonlethal
Defender: The defender can place dispensers in front of them when crouching, they block the defender and zombies but not allies; and in addition whenever a dispenser is destroyed it explodes dealing 100 damage and igniting zombies within 250/hu. This ability may be used once every 15 seconds. The Defender has a continuous 33% defense bonus, and regains 25hp any time a zombie breaks a dispenser or dies to a dispenser.
Replaces: Trapper, Carpenter
Favored: The favored is surrounded by an aura of holy power. A favored continuously regenerates 10 hp per second. When they crouch they share this healing with allies, restoring 5 hit points per second to any allies within 1000/hu. Furthermore, they gain a steady increase to their critical chance at the rate of 4%/sec (up to 200%), which drops by 20% whenever they attack (or by 2% for every bullet from a pistol, smg, flamethrower or syringe gun). Any zombie that strikes the Favored is ignited. Finally, their activated ability (usable once every 60 seconds) deals 100 damage to all zombies in a 500/hu explosion and ignites them.
Replaces: Holy, Zenlike
Engineer: The engineer is now his own perk, replacing your perk when selecting the engineer class. They gain access to a functional dispenser and teleporter (up to level 3), and a 100% functional 1st level sentry or minisentry (The only change being that reloading a sentry still has a down-time like normal). However, there may only be one engineer per 3 other starting survivors.
More to come as I think of them.