Okay, here's what I'm going with for now:
* New behavior for the AI! When the player goes on distant deepstrike runs -- defined as having any human military ships more than four hops away from any human or neutral planet -- the AIs both goes on high alert and starts spewing out ships from their home planets (or a random planet if their home planets are destroyed).
** The tech level of the spawned ships will be whatever the AI's current tech level is, plus one (obviously between 1-5). Unless it's an AI home planet that is being deepstruck, or a planet adjacent to an AI home planet (we call these core planets), in which case the tech level is always 5. Watch out for that: you'll want some sort of launch pad within 4 hops of the AI home planet in order to take it without massive pain.
** The spawned ships will be random fleet ships that the AI is allowed to use in waves, and each AI player will spawn a certain number of ships ship per event-second.
** The event-second interval is defined as ( 11 - Floor(AIDifficultyLevel) ). So, for difficulty 7 or 7.6, that would be 11 - 7 = 4 seconds per interval.
** The number of ships is defined as Floor(AIDifficultyLevel/2). So for difficulty 7, it would be 3 ships every 4 seconds, per AI player. On difficulty 8, it would be 4 ships every 3 seconds, per AI player.
** These spawned ships are in free/threat mode, and will eventually attack the human players in whatever way they think will be most disruptive. They may engage the deep strikers, but more likely they will try to kill the planets of the players instead.
** Note that all of these numbers are PER PLANET that has a deepstrike on it. So if you are deepstriking four planets, multiply those numbers by four. It's best to keep your forces together, and make the deepstrike raids as brief and effective as possible to avoid too strong a retaliation against your forces.
** Thanks to many players for contributing ideas that ultimately led to this.
I went with this instead of an AIP-based solution, because I don't want to kill off all deepstriking completely. I just want to make it a more "fun" activity (in the DF sense), where the risk of loss goes up linearly (or worse) as you pursue this particular activity more. And to make the consequences really terrible if you deepstrike the AI home planets.
I suppose I should stop saying "deepstrike," though, as the activity defined in the tutorial is totally okay. If you're within transport range, this will never kick in (well, unless you make a one-way trip with your transports, which can give you 5 hops -- I sometimes do that). Planet hopping is totally cool and a central part of the game.
For that matter, this "ultra-deepstriking," as I guess it should be called, is also totally cool and part of the game (though not as central). What isn't cool is this being just a really easy thing to do. So I was thinking about GTA and Red Faction: Guerrilla, and I realized that one of the things that really makes you feel like someone underground and secretive in those is how "the law" comes down on you if you stir up certain kinds of trouble. But it's this temporary thing that you can strategically do, and then you can evade them and eventually get things back to normal if you survive.
I wanted the ultra-deepstriking to be like that. So here it is: when you go after the AI on most planets, it's like having 4 stars in GTA. Stuff gets intense until you stop the ultra-deepstrike. And when you go after the AI on its home planets, or adjacent to its home planets, the stuff gets...
very intense. You can totally win this way, I'm sure, but it's going to take a lot more care and planning, and you're going to need beefier defenses and better launch platforms, etc. These roving bands of starships heading 14 or whatever hops out will still be just as viable (as desired), but they stir up so much trouble that it's likely to be a kind of hair-raising situation to use them that way.
Which is the goal.
I'll be very curious to see how this changes things for Suzera. I'm sure she'll still figure out a way to keep to the essence of her strategy, which is fine by me, but hopefully it will fix the exploitativeness of it. Which, with all her suggestions, I know she's been driving at in order to keep the game interesting, and not being just being a pushover for her. Should be interesting.