The basic problem I have with this whole argument is that it comes from the direction of "
Hold XXX and coup de grace in combat lead to unfun and easy death of characters, so lets abolish coup de grace in combat."
There are a few problems, starting with the problem of inconsistency. Coup de grace is a rule in 3E that comes into effect under certain circumstances: the victim is helpless (also a defined condition), the attacker takes a full-round action to deliver it, has to stand adjacent to the victim, and leaves himself open for Attacks of Opportunity. These circumstances are the same whether they happen in or out of combat. A rule that said "coup de grace cannoth be used while in combat" would simply break consistency. Attempts at explaining it will (in my experience) not lead to players who shrug and accept it, but simply try to find a way to still get that coup to work ("I'll take two full-round actions then, I'm not threatened right now" or "My character has a whole feat chain dedicated to precise strikes and you tell me he can't find the weakest spot on that paralyzed orc using a full round?").
The second problem is that, based on the premise that coup de grace breaks a handful of spells because it can be combined for essentially save-or-die effects, then so does chucking somebody overboard from a ship, from a cliff, into a lava stream, from an airship, etc, stuff that can be done with a simple trip attack to mobile characters, and without them to paralyzed/sleeping characters. And those are the kind of "action environments" that always come up in D&D adventures at some point. I don't think there are comparable numbers somewhere out there, but I'd not be surprised if scenes like that are about as rare as people setting up coup de grace moments in the middle of combat. And at least Mike Mearls really likes those scenarios, and wrote a whole rule set around them for his
Iron Heroes game.
Replacing the rule with something else will face the problem that it either needs to have a similar effect, or it will change the way the game is played. Changing it to "coup de grace puts the victim at -1" for example will see players equip their characters with items that grant auto-stabilization if that happens to them more than once in their career, and skills like Self-stabilization will become quite valuable.That will turn coup de grace from what it is now, namely a pretty sure-fire way to kill a very helpless opponent, into just another way to seriously hamper somebody. At some point, a D&D character will only be killable by reducing either hit points to -10 in one go, or doing the same to Con (if ability damage will still work), and that really narrows EVERY tool in the DM's tool box down to things that are meant to only injure somebody, no matter what.
The reverse angle, changing the spells so they don't impose the Helpless condition on the victim anymore...well, lets say I'd be curious how they want to explain somebody being completely immobile but not helpless.
Sorry for being so contrary here, but I simply don't want to see a game where something like "I lop his head off with my axe" is answered by the DM with a "okay, 2 rounds later his buddies pour some healing potion down his throat and press the head down on the neck until it has reattached". Some things simply should KILL a character, not just inconvenience him. If the only way to kill somebody in D&D is to slice off his hit points one by one, the game turns either into something very boring, or something very silly with overinflated damage numbers.