I expect that after the tick we will have 4 new colonization carriers available at each system that has finished the initial construction and is moved to bgs. So no big problem, I can just see an abuse of this coming by blocking enemies from expanding by using their carriers for useless systems. That's all and maybe it is already happening...
Interesting.
It's not a particularly effective way of blocking, even so (which is perhaps why it's rarely come up as even an accidental happening)
- you need five clear systems in range of the system you want to block (four to use the carriers, and a fifth that then can't be colonised from that source)
- the carriers return to their source system 15 minutes after the completion of the first construction, so are presumably available for reuse at that point, so you'd need to tie up all four with a blocking Orbis project [1]
- you can't block someone from using the squadron route to colonise a target system from somewhere else, then flip the ownership later (and this route lets you get factions into systems tens of thousands of LY away from their previous presence, even if they control no stations at all)
- it only really affects factions which control stations in exactly one system (because otherwise you need to tie up every carrier in every system they have a station in)
and want their colonies to be near that system
- if you want to avoid Faction A being able to colonise System B, then by
far the simpler way to do it is to launch a colonisation claim by Faction C to System B, and probably even complete it.
I doubt it's something which will see much deliberate use.
[1] If they block with outposts, you could potentially just complete their project to get the carrier back. If it's someone who's done it accidentally, and gone for something reasonable to build, that's an option.