All known forced Go cycles are impossible with this rule. The nature of the rule itself suggests that forced cycles are either impossible or astronomically rarer than they are in Go when the superko rule is not used. Ko fights proceed in a similar way to those of Go, with the difference that captures and moves answered by captures aren't valid ko threats. On the other hand, snapbacks are not possible, as it is necessary to make a ko threat before any consecutive capture occurs.
If a play causes a board position to be repeated, the game will end in a draw. If forced cycles are indeed impossible, this will require cooperation between the players, which shouldn't occur in actual play.
Luis BolaŮos Mures designed Stoical Go in September, 2012. The game is available to play with the Zillions of Games program. All odd-sized boards from 7x7 to 19x19 are implemented, as well as the option to use neutral blocking pieces to change the shape of the board.
tapir: You are aware that you will have many "right to capture" fights? Even snapbacks are impossible in your variant.
luigi87: Not that many, but yes, often a player will have to use a ko threat in a given sequence to earn the right to capture back. The same happens with snapbacks as well. This feature adds a global positional factor to the evaluation of local fights, which needn't be a bad thing. As for snapbacks, I've added an alternative, somewhat more complicated rule that preserves them in their original form (i.e. without the need for intervening ko threats). (Edit: I've deleted it. At least one rare forced cycle would be allowed under that rule.)
luigi87: Eternal life is not possible in Stoical Go.
Sandra: Counter example:
Slarty: This is not a forced cycle, so it doesn't disprove the claim.
Sandra: The other claim was that standard ko rules donít apply. Thatís the claim thatís disproved here.
luigi87: "Standard ko rules don't apply" is not meant as a claim, but as a rule of the game, as in "standard ko rules aren't used". Maybe it's a bad choice of words. Is it? If so, I'll change it. Needless to say, I'm not a native English speaker.
This said, ko rules aren't needed, by which I mean that there are no known forced cycles so far which make them necessary when the game is played to win.
Slarty: It's still (technically) needed to know what happens if a repeating position is played, to define the game. It could be a source of a little confusion though I think the page is clear. (would imagine borrowing chess's threefold repetition = draw in a very thorough description). Anyway, the game should be pretty good. It's difficult to make it the same as Go (in under ten words, at least) - because there can be snapbacks of any size.
A funny variant idea (doesn't need its own page) is to forbid the last player who captured (or the one with the most prisoners) from capturing again. It's sort of like the doubling die mechanic in backgammon.
luigi87: Yes, it reminds me of a set of bizarre finite Go variants that I discussed a while ago on Life In 19x19. In the most basic one, once a player makes a capture for the first time, that player canít create any more groups for the rest of the game. It creates an intriguing build up of tension prior to the point when one of the players decides to make a capture. As for repetitions, you're right. I've just added a rule to handle them.