"ghost factory.. you build units and there gone"
It could be a unique version of cloaking. One could zoom out to see the unit icons (a bit tied to the UI though).
"non selectable factory.. a factory with op things but you cant select it"
Depending on the OP-ness this could be viable. You could relocate the units with lobsters, transports, gravity guns, or maybe even djinn teleportation. Also, I am assuming that the factory itself is selectable.
"not-a-factory factory.. its not a factory but it insists that it is"
I'm not sure about this one.
"exploding factory.. plopping this is self trolling"
Not necessarily self trolling, imo. I can see a 1v1 comm rush where you attack the enemy comm with a factory plop (I assume this factory would explode stronger than the others).
"long factory.. model is 10 factories long ..."
There may be some niche uses for this, perhaps for a defensive wall untraversable by spiders. The primary issue would be on a small map the model may extend into the enemy base and may get attacked, so I am thinking it should have at least double the HP of a normal fac.