[Lemmy]

I'd also like to be able to build multiple space yards on planets, with the same result. I don't care about multiple build queues, but the speed would be worth it.

Perhaps, for a mod, a "Space Yard Expansion" component / facility, that adds SY rate to pre-existing space yards (and adds slight repair capacity as well), without functioning as a space yard itself ... ? Say, extend the Space Yard tree, and get SY Expansion I through III, each one good for ... um ... 1/4 to 1/2 as much as a SY of the same rating, both in terms of production and in terms of repair?

I believe SJ found a way to do this, SE4 won't allow you to build a new facility with the space yard ability if there is one present, but it will allow you to upgrade a facility to another facility with the space yard ability.
So you would have to mod a facility without the spaceyard abilty, and let that be upgradeable to a space yard facility.