You could but you'd be certifiable! Pay cut to go RHS Airbus! Theres no requirement to do Right to Left on Type at all, Command course can be with the type rating. Just stay on the 74 until your command comes up
But to clarify you said SH command is maybe only 7 years, whereas longhaul is lets say 15 for arguments sake? So if you were to move after year 5 from 74 to 320, would be a paycut in the first instance but if you got the left seat 2 years later im sure it would work out plus you could possibly transfer back at a later stage as a captain?
cheers