I've been thinking alot about rules subsystems, particular in regard to breaking d20 out of the fantasy genre.
Combat in d20 is really a subsystem; it has its own set of variables and rules; it allows for a variety of options within a combat and differentiation of combat roles and specialties between characters, either as opponents or allies. Spycraft does the same thing with chases.
A subsystem makes a task interesting, allowing for enough differentiation in that kind of activity to make repeated instances of it still exciting.
There are lots of considerations in this question. I always laugh when I think about picking up the Star Wars RPG and seeing that Stormtroopers have Profession (stormtrooper). I think I understand what they're trying to do (maybe the bureaucratic elements of the system), but it seems like what it is to be a stormtrooper has already been broken down by the system into attack bonuses, intimidate bonuses, feats, and the combat system in general.
I consider the lack of these subsystems a problem when simulating certain genres; in a science fiction setting, it would seem that something like computer use or starship repair would be important enough of an event to have a subsystem that makes such problem solving interesting. It's just not fun to be playing a sci-fi game, with your broken starship hurtling towards the sun, and to reduce the fate of the game to a single die roll (or even a complex skill check). Forget the consequences for the campaign in particular; what I'm talking about is that here we have a pivotal moment within a certain genre being decided by a simple "roll high" mechanic.
It's as if one were playing a D&D campaign and allowed the characters to make a Profession (adventurer) check vs. a dungeon's DC to determine whether they successfully looted it and killed the monsters. That is fine for tasks not central to the genre in question, but not for anything which is genre-defining.
So what I am wondering, and I don't have time at the present to explore myself, is whether something like computer use could be broken down into abstract categories like Spycraft does with chases, covering things from hacking to programming to repair. The same might be done with mechanics. Ideally, the systems would be so abstract that it would not matter how advanced the technology was; a well designed set of repair mechanics might work as well for a steampunk game as for Scotty on the Enterprise. A good set of gambling rules could be used for poker in 19th century San Francisco and sabacc on Coruscant.
A big concern for any such systems would be plugability; it would be nice to be able to adopt the gambling rules the day they come out, without having to substantially rewrite characters in an existing campaign.
For instance, maybe computers would be broken down into subskills, just like AC, saves, attack bonuses (ranged and melee), speed, and initiative are different bonuses in combat. X ranks in Computers could give you aX subranks to divide among Computers subskills, allowing characters to be differentiated and to facilitate a variety of action options in task resolution.
Edit: Also, plugability is important because sometimes I might want to have a simple computers check for a mundane task, like opening a door.
Another concern, since most of my examples have been cerebral actions (though there is certainly room for physical subsystems, like sports), is how much to leave for players to figure out (like giving them a riddle) and what to leave to an effective use of game mechanics, like in combat.
So, yeah. Maybe that's worth thinking about. You're certainly good enough to pull something off that could add alot to the game.
I would buy a book with a handful of subsystems (like TFT) to expand the genre options for d20 in a heartbeat.
