furbster: I also think that both versions could coexist. But the one with the knight-jump should be the one called Ataxx. Otherwise you'd just confuse people coming here for the first time, especially if they already know how to play the game.
Name the current one Straight Ataxx or whatever, but don't give an alternate name to the standard rules.
Fencer: To avoid regular mixups of rule changes in the middle of the game, and to avoid restarting all games all over again, maybe just rename the current one and create the real ataxx version as a new game, if you decide to do so. Of course that would imply retranslating some tokens... :/