I almost dismissed that as the jest it was meant to be, but it got me thinking. Boards of 1 X 1, 2 X 2, and 3 X 3 are trivial from the start. A 4 X 4 will be too since there's only a few captures to be made and then the board is full. 5 X 5 will probably be like that, though a five in a row can be formed. 6 X 6 gets a little more interesting, but it seems to lead to a block too. I suppose if one was really going to play a game of Keryo on such small boards you could make a rule about who wins if all the spots are taken. There's also the possibilty that a position could arise that you could swap captures until 15 dudes are bagged. I'm thinking that the game would take a minimum of a 9 X 9 board to even closely resemble the play of a 19 X 19 board. Perhaps 10 x 10 would be a good minumum game as it would allow either player to form a five in row from the center four intersections. Going the other way, after the board gets to about 25 X 25 the sides no longer seem to matter.
An alternate rule for a smaller board could have the edges wrap around to touch the other side so a five in a row could have three on one side and two on the other. This would have the effect of making the board play larger than it is and would seem playable on a small board.
I would like to try some of these smaller boards just to see how it would go. If it ever comes up that it can be played here or IYT or elsewhere and anyone reading this would like to play some small board games with me, please drop a line and we'll give it a go.