I think factories on ships would be cool because I think giant ships should be encouraged (if they are soon able to be built)
If had last week a conversation with my friend about this exact topic, though we were talking about implementing a small automated refuelling and refreshing factory within a carrier. There arent going to be ships in a similar scale as the Exekutor.
Why?
Lemme list some points:
1. They are impractical to fly around since (even though there are less astroids outside of the belt itself) there are asteroids as far as i know everywhere
2. But what if there is enough space to fly around one of those things. Well this ship would require a extremely large amount of fuel, fuel rods, spare parts and personell. This means the ships base cost would be in the around 100.000.000.000.000.000.000 plus a daily of lets be optimistic 50 million. Plus you will have to have either very much automation which requires space, more money, and electricity or you have personell, which considering this is a game it would be very hard to make a 6-hour trip with everyone being online and active all the time (considering you play in the evening or afternoon and have a job). So for any military fleet it would be much more cost efficient to have more smaller ships
3. To the war side of things again. For the argument: "Well giant ships could be built buy non military factions as well". That investment wouldn't be remotely worth it if you were not planning to use it in a military, not to mention it couldn't land on stations itself. Now in a war scenario in star base I would rather have 6 Veneattor-sized ships then 1 as big as a Exekutor. Because more ships means that there is not just 1 bullet sponge, but multiple. Also having more ships means you would have more strategic options other than just being a giant rock in the sky flying towards something. Another point to be wary about is that guns have limited range. You cannot start a battle from 5 kilometers away. You also gotta go in close and personel, which makes it harder to defend ur crucial points.
This is why I believe that giant ships have no other use than for show, or optic or psychologic warfare.
And also to flying factories: I still support the idea of the mine layer type craft, but factories for fighters dont work, especially not if you are attacking the enemy. Instead my friend and I want to focus on a simple 3 piece fleet: a Carrier, a Battleship/Corvette, a Maintenance-Ship/Flying Factory.
As can be seen in this lovely little drawing I made in paint.