Since this post has gotten into Tau systems, electrics and manufacturing
I'd like to make comparisons between the TS AX-1-0 and the TS F-B.
The TS F-B can has either a 14 slot drone compartment or 2 skyspear missile racks. So to 'power' the magnets that run the 2 Macro Railguns of the AX-1-0 are about that size (Power and Ammunition rather). Now, let's look at the other weapon systems: 2 burst cannons and 2 missile pods.
Burst Cannons are your standard that you equip to Stealth Suits or Crisis suits. I think based on the modularity of the Tau weapons they would be self contained, even infantry weapons don't require extra power to fire.
and Missile pods I would assume are much the same way, the only power they need to be told to activate.
They shouldn't be deriving power from the batteries that the Macro Railgun uses, so there must be some other reason.
Well, we're adding a completely new system on to the TS that probably requires much more concentration to fire than the swiftstrike railgun on the TS F-B. The Tau probably had to add other weapons panel in the cockpit apart from the one used to fire the auxiliary weapons.
I would then assume that the reason it can only fire the Macro Railgun is because the system being so intricate needs complete focus in monitoring for the Gunner to fire, and the BC and MP were never designed to be remotely fired by drones.
Although, firing other weapons at a BS of 5+ may be a good remedy to not being able to fire at all?