I'm on board with Ahnehnois here. Especially this: "The basic goal of a health system needs to be that anyone can die, but that some people probably won't. And that battle has consequences." Yes, yes, yes.
The game should focus (IMHO, etc.) on keeping hit points small and I'd strongly prefer the scaling of hit points to be slow or non-existent. Let slowly growing defenses and attacks handle most of the raw power scaling, and breadth and/or depth of character abilities do the rest.
I'd prefer if hit points and wounds were kept separate, with hit points being strongly abstract (basically anything a person can definitely fight past) and wounds, which actually kill or disable, more concrete. (I know and fully accept many people have no problems with purely abstract hit points for everything, but I find it jarring. I'd rather not have the "what do hp mean?" conversation, we all know the talking points. I do think building a very light wound system into core can really help modularization, without being too distracting for those who have no problem with only hp.) I envision wounds incurring when reduced to 0 hit points. This should be a fairly constant threat, but one that can be staved off with party effort round to round, so that much of combat is a dance around taking or avoiding wounds while doling them out. I don't favor death spirals, certainly not as a default. Instead, I would make most wounds go away at the end of a rest, fewer at the end of an extended rest (or equivalent), and occasionally some that are difficult to remove or effectively permanent. In general, I think during the average combat most party members should take a few "rest" wounds, a few should take a single "extended rest" wound, and a few times an adventure someone should take something more significant (assuming survival). The fluctuations are what keeps everyone on their toes, unless someone cuts off their toes.
Furthermore, additional rider effect of wounds can be simple (nothing) to detailed (broken left hand with appropriate penalties), with a campaign norm selected by the DM, and exceptions used as needed (e.g. the effects of some iconic monster attacks).
I absolutely want to keep 4e's trajectory of non-exclusive healing, but give each class its own way of dealing with this system. I have a philosophy that the major use of magic, or at least utility magic, is to adjust the typical "fast, cheap, or good (choose two)" considerations for the situation at hand, where the mundane method sets the baseline. Therefore, while mundane healing of wounds might be cheap and good, in-combat magical healing is fast and good, and ritual healing splits the difference. Fighters and bards, on the other hand, settle on fast and cheap, letting themselves or others temporarily ignore wounds, and so on. Thus, a cleric's "cure light wounds" in the heat of combat is an event, and "cure critical wounds" might count as close to a miracle, but characters normally fight and function without it. So no one has to be a heal-bot, but for many classes it is possible to go in that direction if they don't mind the opportunity cost.
In addition, some classes or characters might focus on hit points rather than wounds, and vice versa, but everyone interacts with both at some level. Among its virtues, this can support flavor distinctions that have been problematic to some (like me) in earlier editions. For example, a cleric of Pelor might concentrate on instant wound-healing abilities, while a cleric of Gruumsh might give allies lots of hit points (filling them with hate, for example) but not have the ability to perform instant wound healing. The injured don't deserve it in Gruumsh's eye. So in their own way each is meeting the mechanical needs of "healing" in combat. And outside of combat, someone in the cleric of Gruumsh's party probably has the mundane healing skill, enabling that very evil party to continue on like any other.
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