I've had a couple chances now to play with the Inexhaustibility proc from SMoReichsman runs (one on a level 50, and one that I passed to a mid-20s alt), and I think it may be in need of a buff. First, 30 seconds out of combat to start getting procs seems a bit on the high end, especially considering how fast most teams tend to run in this game (outside of SM runs especially, but even while running one 30s is a good chunk of time). With absolutely no extra Regen outside of the inherent Health and Stamina, you'll regain ~20-25% health and stamina before procs begin processing, depending on slotting and toggle drain (it's 48s to go from 0-100 endurance with no toggles on). After that, procs activate approximately every 8 seconds (7.5PPM?) for 18% hp or 10% stamina, but not for both. It also appears, at least anecdotally, that the odds are weighted about 2:1 or 3:1 in favor of HP over Endurance. My experience has largely been that I finish combat with either enough health/stamina that I'm back to full before the procs begin, or low enough that I want to just activate Rest (which results in being back to full before procs begin). I have not yet had a time where I want to activate Rest and had it still be on cooldown from the last time, which may be where this proc shows it's best benefit.
Given the difficulty of obtaining this enhancement, I think it may be in need of some tweaking to bring it into balance with the difficulty required to earn. I would suggest either lowering the time for procs to begin to 10 or 15 seconds, or having the proc trigger both the HP and Endurance at the same time. I'm also not entirely sure that both would be too overpowered, considering the difficulty required.