How is that any more complicated or bookkeeping than THP and HP already co-existing? You are technically supposed to be tracking them separately since THP does not stack, so you have to keep track of the THP you have to prevent THP stacking.
It's essentially a third kind of hp. You have your current hps, which healing just adds to, you have your temp hps, which don't stack & don't wake you up, then you have these other hps that don't stack, but do wake you up, and then just add to your current hps if there are any left when your rest. What happens when you have a few of these temps, then get a larger pile of regular temps? Do they disappear? (if they do, are you now unconscious?) Is damage taken off the larger pile of temps first, until they're equal, then off both? Do the temps not-stack separately, so actually do stack?
That gets tricky. It still doesn't work well with people who want meatier hp.
Neither do HD, death saves, overnight healing, or Second Wind - and none of them are options that can simply be ignored at the player level by simply passing over certain choices (there's no alternative feature to Second wind, the rest are universal - the DM has to employ a module or otherwise tinker), while Inspiring Word /could/ be just one among many choices in a list of apprentice-tier Warlord maneuvers.
And since the thp become hp tracking the separately just becomes bookkeeping. It just seems like it'd be too complicated and problematic.
Yep, whereas simply restoring hps works smoothly as an established mechanic.
So you have the effect of the warlord shouting and inspiring before combat - the standard rallying cry seen in fiction before a battle. Temporary hit points are a great representation for the warlord psyching people up and allowing them to fight longer than they would otherwise.
Rallying is more in the midst of battle, when things are turning against you. But, yes, for before-battle inspiration, Temp hps are a good model, and an option the Warlord should absolutely have. For rallying /in/ battle, restoring hps works better - of the two, and creating a new kind of granted hp carries bookkeeping and complexity baggage.
So the cleric sits around after combat healing injuries, while the warlord shouts at allies at the start of combat or gets them up again after a big hit.
If you had both in the party, they could specialize that way, yes. The Cleric could take Prayer of Healing and the Warlord could take some Temp-hp-granting St. Crispin's Day speech thing. If you only have one or the other, though, the player should be able to cover both forms of support.
Oh, and it also means if you have a cleric and a warlord in the party their abilities complement each other instead of competing.
I suppose if you took enough spells away from the Cleric, and enough options away from the Warlord, you could create a separate niche for each, such that parties couldn't get by with one or the other as sole contributor of support to the party. You'd have to further niche-limit the Bard and Druid, as well, I suppose. Doesn't sound like a great idea compared to just letting all 4 have reasonable customizablity and flexibility.
a) presumes people are either warlord fans or hate martial healing.
That is a crazy assumption. Most people would be neither, having never even heard of D&D, and it's likely a majority of D&D fans don't much care, either. OTOH, it is pretty safe to assume that people who vocally hate "martial healing" also vocally oppose the warlord.
b) presumes temporary hit points are inferior. They're not.
They are /different/. Temp hps can exceed your max, but don't stack and can't wake you up.
Regaining hit points and temporary hit points each have their strengths and weaknesses. They're situationally stronger and weaker. But there are situations when it's better to have temporary hit points.
Temp hps work well as damage-mitigation, and there's lots of forms of damage mitigation among the existing support classes, in addition to all of them being able to restore hps.
Being restricted to only one or the other would make for an inferior support class.
c) presumes the intent is to make martial healing inferior to magic. It's not.
You very rarely see a proposed solution that would make the warlord balanced with other support casters, let alone superior. If everything you propose would tend to make a non-casting class strictly inferior to casting classes that make the same sorts of contributions, your intent doesn't really even matter.
And it's not about making martial healing inferior. It's about making it different
Meh. Restoring hps is a very bland mechanic. There's no way nor need to make the /mechanic/ different. Make the classes and the way they invoke the mechanic different, and you're there. A Cleric calls upon a deity for the power to cast Cure Wounds, a Bard uses arcane lore and the power of words to cast the exact same spell, and is sufficiently differentiated. A Warlord's Inspiring Word is already better-differentiated simply by not being a spell, at all, and could be further differentiated quite a bit - tapping HD, basing healing on the target's as well as the warlord's level, etc - without actually undercutting it's usefulness by making it do something other than actually restoring hps.
