As PC’s progress, falling to 0HP in combat gets less and less meaningful. So I have used a rule that whenever a PC is at 0HP at the end of their turn, OR fail a death save, they take a level of exhaustion. It makes the 0HP yo-yo more dangerous, and makes it so “death” has some longer term consequences.
That’s a good idea. I tried doing something like this in a one shot once as a test : Any PC or monster could voluntarily delay their initiative to anything lower than it currently is. It was a disaster. Very hard to keep track of and exploitable with spells, like you mention.
But restricting it to the first round and making it permanent…that might work.