GURPS may or may not be the best way to go about this because, as mentioned, when things don't scale well at the high skill levels, and game-play is kinda slow given you've got to roll a bunch of dice and do a lot of math for a single attack.
Rolling dice and math
shouldn't be an issue 'cause we can do at least some of it programmatically.
e: TBH though I don't think we'll be finding a system we're truly satisfied with :/
e2: GURPS, from what I've seen, will resolve the technique/seal-creation problem, but it's not really gonna make option creep any better. I'm also not particularly familiar with the probabilities involved in dice, and the system overall is more suited to players actively choosing what their characters do, with regards to their options.
e3:
So, some thoughts. It's probably possible to modify GURPS to our ends (I mean, that
is what it's meant for), but it'll require some effort.
For instance, I'd like to just port over the skills/XP system we've been using, rather than having to learn a new one, and just using the GURPS conflict resolution system instead. This also has the side effect of keeping the general progression the same, insofar as genin/chuunin/jounin, etc. goes.
HOWEVER, in order to do so, we have to figure out what to do with attributes, because in GURPS, all skills increase along with their attributes, and on top of that we'd need to figure out what to do with the attribute requirement system.
It's kind of a... project. But I don't think we'll be able to find a satisfactory system without major overhauls to it. Hopefully I'm wrong!
e4:
I had a thought. I can't remember exactly what Hazou said, but he thought something to the effect of techniques keying into the same thing as seals, right?
Technique Hacking (from what we've heard) doesn't seem to cause the same class of failure ass seals do. Sure, Technique Hacking Failures can kill the user, but as far as I know, it's as a consequence of what the technique does (ie, an earth technique failure might replace your blood with stone if you make a mistake in its formulation), and is limited in effect to the user's chakra pool in a way that seals aren't. Technique Hacking Failures generally cause behaviour defined by the technique's intended effects as opposed to the undefined behaviour seals exhibit.
This being the case, a possibility as to how the Hiraishin Technique works:
HT uses the Hiraishin Seals as a method to bypass the Chakra Diffusion problem. Hiraishin Seals, each identical and infused with the user's chakra, serve as beacons in the Out, that HT detects the location of and uses the "hole" in the out that they make to determine their location in the elemental nations, then teleports the user there. The teleportation itself is straight chakra magic, probably a THed substitution technique.