For an upcoming campaign I'm considering a set of hacks to give 5e a more visceral sense of danger. One such hack would eliminate the incapacitated condition altogether and use stunned in its place. If it isn't obvious, the goal would be to heighten the vulnerability of a combatant rendered incapable of acting. What game-balance pitfalls would likely result from such a rule?
To elaborate: incapacitated is already subsumed within stunned, so the only balance issues I foresee would involve game elements that impose the incapacitated condition without also imposing stunned. For example, hypnotic pattern imposes incapacitated but not stunned, and as a relatively low-level spell, it conceivably might cause problems for low-level parties. Then again, hypnotic pattern is arguably overpowered already. Granting advantage to land a single hit on a target affected by hypnotic pattern probably won't worsen that problem much; at most, it'll just hasten an encounter hijacked by hypnotic pattern to its conclusion a bit faster.
Surely, however, I'm missing something. What am I missing? Pitfalls involving fiends would be of special concern, as the campaign will include Descent into Avernus.
(Note: I'm not interested in frame-challenge answers. I know there are other games that do this or that better than D&D. I routinely advise people who propose hacking D&D to make it more this or less that that they might be better off just finding a different game. In the grand tradition of not following one's own advice, I'm considering this house rule anyway.)