In my game i have lots of rebellion ongoing in the Core Worlds, never had this before.
Rebellions are new in 0.9.6, yeah. They always happen after a successful invasion (unless it's a faction retaking a planet that originally belonged to it), and can also happen over time when stability stays low enough for a while.
And i say it again , when Faction A announce to invade a Planet from Faction B , normally Faction B would get some sort
of Special Fleet , but not now.
Not sure what you mean by "special fleet".
Defense fleets in response to invasions will silently* spawn if brawl mode is enabled in config.
The new special task groups may also appear during an invasion or raid, although whether they'll show up depends on several factors (they need to exist in the first place, then the target needs to be more important than anything else they might be doing right now, then they need to get there in time...)
*there's a bug in the zipped version that makes them non-silent, but the hotfix .jar fixes this
Also there were 2 or more special events , where colonies were completly wiped out , i don`t know why.
Colonies can decivilize (vanilla feature) if they're at zero stability for long enough, that may have been what happened.
Also if a faction decides to saturation bomb a colony and it's size 4 or smaller, it'll be instantly destroyed.
Is this being considered? If it is, can we also have an option to sell ships to an up and coming invasion fleet? You know like the trade missions where we deliver supplies and goods but this time we deliver slightly-used/pre-loved (read: structurally damaged) Onslaughts at premium prices for more war profiteering enjoyment?
- Invasion spawn frequency and (to an extent) maximum fleet size already depend on the faction's industrial production, as noted in a couple of the recent previous posts.
- Ship procurement missions sound neat

I'll look at them some time down the road.