Here's the gist of what I discussed with Arch in PMs.
What does banning those mods mean?
A: Remove them from the vault
or
B: Track down players who use them and slap them with a ban
A is very simple to implement but also doesn't accomplish much. Players will be free to share, install, and use these mods, just won't be through FAF servers. If you truly believe they provide enough of an advantage to be called cheating, then this would do little to solve the problem.
B would actually solve the problem but would be immensely difficult to implement. UI mod usage is not reported back to the server, so it would require reporting by players (who are what, zooming in to see if mass fabs stop spinning every few seconds?) and then processing by moderators. The mod team already has a ton of work to do, and a significant backlog as it is. Even if we were willing to go through all that it would greatly slow the processing of all other reports, many of which are more significant than "this guys mass fabs are toggling".
A? Yeah whatever, don't think it matters much either way
B? Absolutely not. While I agree these mods do technically provide an advantage, it's minuscule compared to the effort needed to put a stop to it