In what way does the existing special forces not meet this description? Not protecting all planets?
In retrospect, it does meet that description fairly well. The idea behind it can be difficult to see; as the player doesn't always actively see movements of the special forces fleets.
I could say, from my perspective, that they could be more responsive to incursions, but I honestly haven't played anything resembling a genuinely challenging game (from the game's perspective - from mine, easy 7's are still a bit awful), so I don't think my opinion is quite valid.
The idea of a H/K AI is a tad entertaining, though.
Increasing their responsiveness might be nice.
One way this could be done is to let the special forces be split into N different groups, each group could choose their own special forces guard post to gather at, usually across different planets. This will, on average, increase responsiveness, even though each "wave" of them may be weaker (which is a good reason not to set N too high).
H/K on dynamic defense is also intriuging. Maybe allow the AI to spend a large number of their "points" in their strategic reserve to make a (or serveral, if it has enough) H/Ks.
On higher difficulties, allowing them to "spend" a bunch to put a few in special forces may be cool too, though there would need to be a galactic cap for number of H/Ks in special forces.
Heck, why not find some sort of trigger that will prompt AIs to stuff one to a few H/Ks in threat fleet, if the player starts to really annoy the AI (and the difficulty is high enough)?