Ugh, 11 pages before I was able to get back and reply to this. I may have to revisit this thread at a later time when I've had time to really digest it. But I want to respond to a recurring theme I see:
Yeah, honestly, I see DnD as a heroic game. It's pulp fiction action books. The character can have their leg broken and a chapter later jump from one ship to another - a good player will wince in pain and keep going, but at the end of the day, you're heroes and this is a movie.
This has me scratching my head. In what movie about heroes do the heroes heal all of their wounds overnight without the aid of technology or magic? My experience reading and watching about heroes is that they
must at some point suffer through adversity or pain (that which cannot be resolved automatically overnight) in order to prove that they are heroes within the story. What you are describing to me sounds more like superheroes when they are fighting normal criminals. And even superheroes, when faced with a real threat, suffer issues such as losing their powers, acquiring vulnerabilities that can be exploited, etc.
So, the explanation that automatic nightly regeneration of HP is because they're heroes doesn't adequately explain this for me.
That being said, I do agree that part of the issue here is the abstraction of HP. I'm not going to go into that subject in any detail because it could be its own 100 page thread (and it has been, time and time again). However, I'll agree that because HP is such an abstraction, it's a challenge to have a healing system that pleases everyone. You have problems on both sides:
1) You can allow HP regen overnight, and you can argue that this works because the HP were never wounds in the first place. But what you sacrifice here is the capability for PCs
to be able to suffer wounds. You also create the problem that healing magic isn't actually healing anything, it's simply restoring stamina, or mental fortitude, or whatever it is that you imagine is being expended when HP are used up. Essentially, the PCs never suffer any harm. I find this to be a very unsatisfying way to tell stories about heroes. It's more like a Saturday morning cartoon.
2) You can allow only a very small amount of HP per night, and you can argue this works because it allows for PCs to suffer wounds that require natural healing. But what you sacrifice here is that HP are supposed to represent more than just physical damage, and also you sacrifice the more heroic mode of play where,
most of the time, PCs don't have to be sitting in a hospital for weeks on end, and can continue having adventures (without a dedicated cleric-healing-bot).
I see neither solution to be sufficient. I like someone's idea about splitting out Vitality and Hit Points like the way the d20 Star Wars RPG did it. I think this is the house rule I would try:
Hit Points: All characters begin play with 8 Vitality points (plus Con bonus) at level 1, regardles of class. Starting at level 2, characters gain Hit points according to their class rules.
Damage: When a character takes damage, remove their hit points, first. Once hit points have been depleted, begin removing Vitality Points.
Death: When a PC suffers damage below 0 VP that is equal to their amount of VP+HP, they are instantly dead. Otherwise the rules work the same as 5E.
Healing: Short and Long resting works as per the 5E rules with regards to hit points and hit dice. Vitality points are healed at 1 point per full night of rest, or with magic. When using magical healing, vitality points are always recovered before hit points.
Direct Damage (optional): You could rule that certain damage applies directly to vitality, such as falling, if you want to*. You could also rule that instant death from said damage occurs when the damage goes below 0 by an amount equal to their Vitality (rather than VP + HP).
Wounds (optional): I am not stopping to think about this in detail yet, but you could have a system whereby whenever vitality damage is suffered, there is a chance the character suffers a wound that must be healed. I would say the healing occurs once they have recovered back the VP level they were at before they suffered the wound. Ex. If a character with 8 VP takes 6 damage and suffers a broken rib, the rib will heal once they are back at 8 VP again.
Those of you who already worry about level 1 being so dangerous for PCs, just start play at level 2, or give the PCs a level of HP on top of their VP. I don't worry about this because level 1 being dangerous is a part of my style of running games. Actually, I might run the game at level 0 before hitting level 1, where they not only get HP but they get their class features. So at Level 1 they would be stronger than usual 5E Level 1 characters but they had to get through a very deadly Level 0 before they made it to that point. It's a game that starts out gritty but transitions into being more heroic.
Edit:
*Thinking about the math here a bit more. A character that falls 20 feet would take 7 damage on average, meaning most likely they will still be concious but gravely wounded, and in the worst case they would suffer 12 damage, meaning they could never be killed from this height. It's not until they fall 30 feet that a level 1 character could actually die, but that would be a 1 in 216 chance, so it's not likely. Once you get to 40 feet, the average damage is 14, and the chance of outright death is pretty high. Breaking this down:
Falls (For characters with 10 or 11 Con)
20 feet = Likely gravely wounded but still concious
30 feet = Likely gravely wounded and unconcious
40 feet = Just as likely to be gravely wounded or killed
50-70 feet = Most likely will be killed but could survive
80 feet = Very unlikely to survive a fall from this height
160 feet = Completely impossible to survive a fall from this height
This seems plausible but gritty. If you wanted to have falling damage apply directly to VP for some realisim but still want your game to be heroic, I would recommend 1d4 per 10 feet for falling damage.