The structure won't support a 5" gun and the magazine would be a major redesign, but also no targeting system or sensors to go with it (or bunks for operators/maintainers).
It'll be a common naval gun though, so should be lots of lessons learned from other navies using it, and honestly the transition from the old 76mm to 57mm didn't seem too bad as would just be part of the transition training from CPF to CSC for the crews.
Common equipment works well when you have common requirements, so may end up with common equipment on AOPs and JSS, but very little with CPFs and CSC, as the gulf between non-combatants and combatants can be huge.
The other thing with common equipment is some of the kit we're using dates back to WW2 (or the days of sail) so it's a chance to push the reset and change some traditional things as there is a lot of better kit available that also works better with smaller crews.
