I'm going to put this here, since:
1) All of the people I know of who are deeply invested in aura-based homebrew character classes are here.
2) I haven't gotten around to updating things on the new/old/recovered board yet.
Please let me know what you think. These are just my current thoughts on the matter, not final changes.
Motivate Endurance: Allies gain a bonus to their Armor Class while the ally has half of its maximum hit points or less. Allies within the aura that are reduced to 0 or lower hp automatically stabilize, can act normally, are are not at risk of damage from performing strenuous actions. While at 0 hp or lower, allies gain 5 temporary hit points per point of your aura bonus each round at the beginning of your turn. These temporary hit points last until the beginning of your next turn (when they are granted anew). Allies do not die and are not destroyed until their hit points are 5 lower than normal per point of your aura bonus.
Current thoughts on the matter of Motivate Endurance: The current version (above) seems like it would be too potent in the earliest of levels. Thanks to the Diehard aspect, there's an extra 10 hp to work with in a pinch for everyone in the party (at least until the marshal himself dies). It's a risky 10 hp, since you're eating into the buffer between unconsciousness and death, but it's there, and with it the aura effectively adds 15 hp to your staying power right at 1st level. There's also an inconsistency in power level, as nonliving creatures don't actually get that extra 10 hp buffer to use.
Also, technically, Motivate Endurance has a similar problem with nonlethal damage as Diehard from the PHB does. Any nonlethal damage is greater than your hit point total if you're at negative hp, so you fall unconscious anyways. That, or you're functionally immune to nonlethal damage, but only when at 0 or lower hp. Either way is inane.
There's also a small issue of Motivate Endurance functionally adding to your hp total, yet not really doing so, thus allowing it to stack with things that actually do, like the Tough It Out minor aura, which it shouldn't stack with.
One last thing, not directly related to the rebalancing effort, is the way temp hp gets granted. It's entirely binary, meaning that 1 hp difference can grant you 5 or more temp hp each round. There's also a little confusion with the timing, as there is either a theoretical moment where you've lost the previous round's temp hp but haven't received the temp hp for the new round, or you might not actually get temp hp in the new round at all due to the remaining temp hp from the previous round pushing you above the threshold. It's bugged me for a long time, but it never seemed worth the effort to rework on its own.
Proposed changes: Essentially rewriting the aura's mechanics, although keeping to the same concepts. Remove the Diehard aspect (conscious and can act at negative hp), although keep the automatic stabilization. Change the extended death threshold thing to a hit point bonus instead (similar to the Tough It Out minor aura). The temp hp at 0 or lower gets rejiggered, too. Note that the change from extending the death and consciousness thresholds to adding hp directly means that the AC bonus on 1/2 hp doesn't kick in until you've taken slightly more damage than before.Motivate Endurance:
Allies gain a bonus to current and maximum hit points equal to five times your aura bonus. These hit points are not lost first like temporary hit points, and disappear when the aura is lost. Allies with half their (newly increased) maximum hit points or less gain a bonus to their Armor Class. Allies reduced to 0 or lower hit points automatically stabilize. Each round at the beginning of your turn, allies with fewer hit points than five times your aura bonus, excluding temporary hit points, gain temporary hit points equal to the difference. These temporary hit points last until the beginning of your next turn as new temporary hit points as granted, or until the aura is lost.
Note: These changes would also apply to Pain and Suffering (divine mind mantle aura) and Stamina (dragon shaman draconic aura).
Side note: Add in a bonus to Endurance-modified checks/rolls (as the Long Haul minor aura) as an additional minor benefit. It's thematic, if nothing else, and it feels weird to have an aura called Motivate Endurance not boost Endurance. I believe the standard for secondary skill boosts on major-tier auras (divine, draconic, major, mantle) is 2x the aura bonus.
Edit: Forgot that sufficient temp hp will make you conscious, which defeats the purpose of removing the Diehard element from this rework. Need to either rework the temp hp part, which would probably make an aura with lots of moving parts even more complicated, or replace it with something else entirely.
Inspire Pain: Each round at the beginning of their turn, enemies in the aura take damage equal to twice your aura bonus. This damage can be either lethal or nonlethal damage, chosen when the aura is activated. You can change this selection as the same type of action as activating an aura. This damage is not affected by damage reduction.
Inspire Pain and the auras like it for the divine mind (Death, Fire) and paladin (Wrath), are intended to provide a small but consistent source of damage to nearby enemies. They are intended to build up damage across multiple foes to aid the actual attacks and AoEs in dropping them, similar to how damage buffing auras do, but along a different vector. The auras are only intended to actually finish off enemies that have already been weakened by attacks that nearly, but not quite, dropped them already.
Inspire Pain's damage value is low, but unlike the similar auras of other classes, is available at 1st level, when monster hit points are also low. At higher levels, the damage the aura deals is insufficient to drop all but the weakest of enemies in a reasonable time frame, but CR 1/2 and lower monsters can often have 6 hp or less.
Proposed changes: The damage trigger changes from the beginning of enemy turns to the end. This gives enemies one extra round of actions before being dropped, and allows some counterplay by allowing them to flee beyond the range of the aura in order to avoid the damage before it triggers.
Note: These changes would also apply to Death, Fire (divine mind mantle aura), and Wrath (paladin divine aura).
Motivate Retribution: Melee attacks that hit allies cause the attacker to suffer 1d6 damage per point of aura bonus. This damage is not affected by damage reduction.
Motivate Retribution's reactive damage is a concern, much like Inspire Pain's automatic damage. The numbers are larger, although the triggers are less frequent. Motivate Retribution also has a slightly more direct comparison to damage adders like Motivate Ardor, which add +1d4 damage per point of bonus to allies attacks.
Against any melee attacker, Motivate Retribution is guaranteed to trigger if the enemy wishes to actually do anything in the fight. If the attacker needs to trigger the reactive damage enough to be dropped himself in the process of dropping a PC, then the battle is effectively won automatically by the Motivate Retribution aura, and that's a bad thing. Small hp pools, small to moderate damage values, and a prevalence of melee attacks (as opposed to ranged or magical attack vectors) at low levels make this a concerning issue. The variance in the retributive damage, and in standard damage rolls, does make an absolute guarantee of this much harder, at least.
Proposed changes: None yet, although I'll be keeping my eye on this aura's potential.