Panicking that NOD getting literally anything into space means Instant Death/Loss is a bit too much catastrophizing. It also assumes that Kane wants NOD to just brutally destroy the entire mass of all of GDI's holdings, which...doesn't seem likely.
This. Remember, Kane's canon endgame is to
convince GDI to build something for him. Even if he had the means to simultaneously vaporize every GDI thing from orbit with nuclear carpet-bombing, it'd just leave him fucked over on the ruins of a burned-out planet that would rapidly be eaten by tiberium.
What he needs is either to convince us to build the TCN, or to conquer us and
seize the means to build the TCN. Either way, he has to let us retain the
capacity to build the TCN. In principle he, like us, has a "space colonization" endgame where he fucks off into space with the Tacitus and figures out his ascension goals from a Mars base or something, but it's more remote for him than it is for us.
Tiberium Mutation Stabilizers have the form of a satellite network. Which is something Kane will want to take out to accelerate his timetable.
Debatable. Remember, Kane's plan isn't actually "cause world to be eaten by tiberium." At most he wants tiberium to exert pressure on GDI to do things his way... but he can't have tiberium be in a position to eat GDI before the job gets done, either.
The stabilizers
concern him, but not because they exist. It's because they imply that GDI may be figuring out more about tiberium, enough that they need him less. It's the fact that GDI
can build them that might concern him, not the 'need' to destroy them.
But yeah, we need space-based laser systems (to defend our own orbitals) and space-based impactor systems (to provide orbital bombardment support). This is reasonable, we just need to commit actual resources to the task, which isn't fun but we can do it.