Well i can safely say 24/7 is not for me. Im thinking the reasons are pretty much the same as yours. But i have come to formulate it differently.

To me the fact that my sub is one person in play and a different much more dominant and image aware person outside. Well that is my actual kink.

I have had a 24/7 sub and what happened was i came to think of her as a constant strain on my imagination and life in general, simply because i felt i had to judge myself for every command and decision, instead of just going with it and maybe finding out not to do so again in debriefing.

Im not saying its the same for everyone, probably the issue with my 24/7 relationship was her basic lack of individualism and me overthinking it.

If your not ready to take on the task either for lack of desire or insecurity. Then dont ruin a good relationship by changing it. Maybe thatll lead to other issues but thats life for you.