Jettisoning the nacelles was considered in TOS' "The Apple" and "The Savage Curtain", but in both cases they never actually did it.

You’re right, that’s the model they landed on by TMP. I meant to say it resonates with Jeffries’ original concept that the engines were just too dangerous to be near the ship, which I always preferred. And who’s to say 32nd century ships don’t have power plants in the nacelles themselves, like a lot of early fandom assumed in the days of TOS? It would make sense if they’re completely separate now. (I know we saw Discovery with a central warp core after its refit, but Discovery is a bit of a special case).