I was just brainstorming, and came up with an idea concerning the Tech Tree, and how it could be improved. I'm not sure if it would work though, here goes my idea anyways.
Upgrading buildings like you can a space station. Lets say you could build a light factory, but instead of making another build slot for your heavy factory, when you purchase the heavy factory it removes your light factory and puts the heavy factory in its stead, with the heavy factory being able to produce all the units a light factory could. Now, I know the drawback to something like that would be that you couldn't have one planet where you make all you're light factory units as fast as possible for deployment. You could workaround that though, I've got an idea as to how.
I would greatly appreciate you're thoughts on this, feel free to completely dismiss my ramblings.
I'm not a master coder but i think it should be possible. However i don't think it is a good idea. When you build multiple vehicle factories you get a bonus in build speed. That would not be possible with your system as you can only build one.
The factories also help in planet defense. They spawn units. The more factories the more spawned units. Again with your system you only get one.
In your system, when fully upgraded, all buildable units would be available. They wouldn't all fit on the buildbar. There are more units than buttons.
If anything i would rather see the opposite. Have multiple spacestations for the different ship classes instead of one upgradable station. Unfortunately, as far as i know the AI doesn't build them so thats pretty useless.
Just my two cents. feel free to ignore.
In AotR 2.50, we have upgrading shipyards in the skirmish. We added the shipyard upgrades for the AI in PurchaseSpaceUpgradesGeneric.lua The first small AI(only AI) shipyard spawn in the near from the spacestation with lua objectscript. The player small shipyard is a normal buildbar object (buidable spacestation).
Actually I've found a workaround about that in my head. When you would upgrade the light factory, to a medium factory, you would unlock another unit, which is like light factory(1). It would be the exact same as a normal light factory, and you would be able to build as many of them as you want. And you wouldn't have a problem with advanced factories, they would be perfectly normal. The unlimited units thing wouldn't really be so much a problem, unless you where adding units to the tech tree, which I'm all for btw. Too bad you couldn't just make it so when you select a certain type of building, which could build the units that the building there... Would make so much easier for additional units
that wouldn't work. they'd be subject to building capacity, and that kind of gets rid of your idea altogether, making it pointless.