I feel like the battlescape incarnation of the 25mm in cars and field guns should be swapped with the 50mm cannon. For one, it feels more right for the field gun to have an actual field gun caliber, 25m in a gun carriage that big is a little comical. The 25mm feels too powerful for what it is, given 25mm HEIT has the same explosive mass as a 40mm grenade (longer shell), so you could leave the stats the same and just change what rounds it takes. Swap the ammo type to a five round clip instead of individual shells, which is always a ballache when using them for craft weapons. It would keep the !Highway House! missions relevant longer, as a single 25mm is often outclassed pretty quickly in the early airgame.
By the same token, it'd be cool to get more battlescape versions of craft weapons. The 30mm or gauss cannon would be cool on tanks and mechsuits, and it would be, extremely funny to give the player a tank chassis that carries a pair of craft missiles as nuclear rocket artillery.
Since we're experimenting with deployable minion units, do we have an Aliens style sentry gun yet?