I have plans along these lines (would probably only affect the combat mod as a game option though). It would do the same with any missile weapon - Once forced into melee range they begin using a melee weapon.
It will consider the 'ammo' as shots per combat before melee becomes necessary. Obviously, only first strike rounds will keep a melee unit out of melee range but once the melee unit closes in, you'd have your distance fighter switching to a melee weapon (unless they have an ability to keep using their missile weapon until it runs out of 'ammo').
So yeah, I'm already considering all this but it would NOT affect a game that doesn't utilize an Advanced Equipments option so should not be problematic for those who want a simpler combat scenario.
BTW, this system of 'Side Arms' would also play a big role in enabling and handling 'Disarming' abilities.