gave one example.. if (when) the K'Khee come it will be a Imperium wide threat when they go blown Ghengis Khan and give a planet 24 to either surrender or get vaporized. None of that lay siege and give Chuck Norris the time to don his cape tomfoolery. Canon has already set it up hasn't it... just up to the 4 leggers to pull the trigger and there wouldn't be much between Capital and Core sector once they ran roughshod over Ley and its underpowered fleets. THAT is a full 5 alarm fire of an Imperium emergency and threat to its existance. Especially as the K'Kree match the Imperium for high tech 15 standard and resulting naval ship badassery... and a whole lot of them...
I am honestly not sure what you are talking about. I can only assume you are confusing the Lords of Thunder, a fanatical splinter faction of the K'Kree that are a small polity of about 3 subsectors' equivalent with the actual 2000 Worlds. Because there's nothing in the K'Kree Alien books or other materials that suggest that the 2000 Worlds is interested in attacking the Third Imperium, much less actually capable of doing so.
Firstly, there are two full sectors of space between the 2000 Worlds and the Third Imperium. There's like 65 parsecs between the two Empires.
Secondly, while there are some TL15 worlds in the 2000 Worlds, the source material says that most of their warships are built at TL12. Because the various Steppelords are only a little more centralized than the Aslan, so they aren't building to some coordinated standard.
Thirdly, even if the 2000 Worlds had the same industrial output as the Imperium (despite being smaller and having a lower population density because of the size and claustrophobia of their population) and everything was built at TL 15, their ships are still massively inefficient compared to the Imperium's. Because K'Kree are very space intensive and they also spend a lot of space on building a prairie in every ship. So every Imperial battleship will have a lot more firepower than its K'Kree equivalent.
The K'Kree are about the same size as the Zhodani, possibly just a little bigger. They are more likely to destroy things in their raids and attacks, certainly. But the idea that they could just roll through Ley and Fornast to threaten Core is simply not credible. The Imperial fleets over there are much, much stronger than the half assed fleets of the Domain of Deneb.
And, finally, this is all a complete tangent. There is no evidence that the call up of the reserves needs to be Imperium wide or triggered by word from the Core. It's 10 months from Regina to Capital at Jump 4. More than 6 months by Jump 6. Each way. The whole point of the feudal-ish distributed government of the Imperium is that the dudes on the periphery are responsible for handling things in their regions, because waiting a year before you even start calling up the reserves is dumb.
There's also the issue that the Fifth Frontier War book itself explicitly states that a massive call up of reserves began almost immediately. (pg 134, if you were wondering).
So I'm not really interested in discussing whether there is or should be a call up of reserves. I was wondering if anyone actually used the detached duty and reserve rules in their peace time campaigns in an interesting way. And, what people were doing or were thinking about doing (if anything) about PC military vets if they planned on using the 5FW in their campaigns, with or without having done any reservist stuff previously.
The impression I'm getting is that basically no one active on this forum is doing anything along those lines, whether out of personal preference or because the all the information on how those things work are scattered far and wide away from the core rules in MgT2e.