Kirk never wore red, except in the GYM! [refer: Charlie X]
Unless you count the maroon in the TOS crew movies as "red"
Probably that. When the ToS movies, and later TNG, etc came along, they switched the gold/red colors around, making red the command career line, and gold as engineering, and apparently tactical as well.
This issomething I've seen a good few threads with a lot of support for, I really wouldn't be surprise if they added it in at some point eventually either in a major patch or definitely an expansion. People want an official xo.
Would be interesting to be able do designate some of the other officers as section chiefs, just for immersion and fun. Give one of the science BO's the CMO title, one of the Tacticals as Security chief, Engineer as ChEng, etc..
Wouldn't necessarily have any extra powers (we don't want to get into some crazy balance issues later), but I can see where it would add some depth to the experience.