I would agree with the resting/healing as one of the biggest adjustments people make. But even that is pretty cosmetic.
But real modifications? We've never seen much progress here. People throw out ideas but nothing seems to stick.
Given that Gygax himself indicated that hit points
mostly represent luck/hero factor/whatever, and all of the character classes stopped increasing HD around 9th level in prior editions, only adding a small fixed number of hit points plus CON bonus after that and given that going below 0 hit points was an optional rule in earlier editions, one could consider a trip point that says "this many hit points represents meat, the rest is luck."
The issue I have with 5e isn't
just that you are 100% until you hit 0 hp, its that you can't be killed until your damage goes to negative your max hit points. You've effectively doubled the scale for hit points and you've made it so that the need for magical healing or a believable period of rest is almost non-existent.
So - a PC that goes into the negative hp region from damage, but not enough to exceed their hp maximum remains at 0 hp and the rest of that damage just vanishes into the ether. Additional attacks have to do at least that PCs maximum hit points in damage to cause death; otherwise it just results in a failed death save - so you'd need at least three attacks to kill an unconscious PC, which seems ridiculous. If that PC takes no more attacks and then stabilizes, and no other healing occurs, they regain 1 hp in 1d4 hours. So they can go from unconscious and on death's door to 1 hp and full capability in as little as 1 hour, even though we know some of those hp represent meat per Gygax. They can choose to "power up" by taking a short rest, for just one hour more and potentially regain
all lost hit points (for argument's sake, I'll assume they burn all HD and recover half of their total hp). They could then take a long rest for only six hours, restore all hit dice spent during their one hour short rest
and all lost hit points. So - from one foot in the grave to not a scratch on 'em in 8 hours?
In my mind, if you don't want to inflict injuries that impact your combat effectiveness as you lose hit points, given the extremely lax healing rules in 5e, why even bother to keep track of hit points to begin with?
You want to keep the healing rules as-is, there needs to be some type of consequences for taking damage in combat for the encounter to have any impact whatsoever. In 1e or BECMI, everything was at stake at all times. As the game has progressed through the various editions to become "more tactical," players can be
less tactical because the consequences of tactical failure have become less and less.