Below is a recent post to the GURPSnet mailing list, on the topic of “Anti-talents” that reverse the effects of Talents.
I have home-brewed “group competences” that are pretty much the same as the Talents that 4e later brought. (4e picks a much better name; I’ll steal “Talent” for the rest of this discussion.)
They all have accompanying “Group Incompetences”, that reverse the bonuses into penalties. The latter make for amusing character concepts (and sometimes amusing trait names), and work as you suggest, but with one big difference: I only award -1 per Group Incompetence, far less than the advantage value of the reverse Talent!
For what it’s worth, my reasons for preferring these to 3e’s Incompetence:
1) I think -1 per Incompetent skill is far too generous. You can easily rack up several points of disad by declaring Incompetence in trivial skills you’d never use anyway.
-1 for an entire group, however, is not a crock. The available groups are generally meaningful ones too.
2) Just as bonuses on a related group feel more sensible than do bonuses on lone individual skills (4e apparently agrees, as that’s how Talents work), penalties on related groups also feel more sensible. (Again, 4e may agree; it appears to have dropped the Incompetence idea, though without yet adding Anti-Talents.)
3) I really dislike the Incompetence disad’s “you can’t learn the skill” restriction. Real life suggests incompetences that you can struggle through; you’ll just always have a real hard time of it. Much more interesting!
A nice skill penalty makes it difficult, though not impossible, to gain competence in the skill. (I hadn’t specifically considered modifications to time required, as you suggest, but that could be done too.)
Best of all, you can still have the oddball character who can’t learn a skill. The character simply doesn’t buy the skill in question, with “can’t” as the explanation. No special rules needed.
So that’s one existing take on “Anti-Talents”. I think 4e could easily incorporate the idea, reversing the effects of all those nifty Talents that 4e and players have come up with. It may even make sense to reverse Talents at 1/5 value, so a 10-point Talent becomes a -2-point Anti-Talent. What do you think?
(Final thought on your suggestions: I see no reason to rule that the character can’t buy off an Anti-Talent. As long as there’s some good explanation, why not?)