I think the weapon types we have now cover the bases. The only thing I'd add would be the different ammo types, with flak being the priority, and perhaps a BA anti-air option.
Beyond that, if I had my druthers, I'd add the following to enhance the mod's polish:
* better flight model (I know 'realistic' is not possible, but I think ASF need more momentum, to prevent the cheesier diving/turning moves)
* increase the Clan/IS differentiation (eg. voice samples)
* more detail on the buy menus, with a 'hover pop up' giving further details of the chassis and loadout
* more varied VTOL loadouts, across the price spectrum
* Mech bay creation/repair animations
* squad (star) designations and communication
I'd love to see a 'Commander' role added, a la BF2142, but I know that's not on the agenda.