I think that Makruk would be a good addition to BrainKing, but I suspect that implementing handicaps and the special rules for checkmating a bare king within a requisite numbers of moves will prove difficult.

As to Chinese Chess, it is a very good game, but maybe Korean Chess (Janggi) would be preferable? It is similar to the Chinese game, but I think that it is a more satisfying game.

Shogi (and some of its worthwhile variants like Tori Shogi) would obviously be great games to add to BrainKing.

Maybe the large version of Mongolian chess called Hiashatar would be welcome? The way that the bodyguard can stride across the board with near invulnerability and its curious effect of diminishing piece power by its zone of influence certainly appealed to me. The remainder of the pieces in this game move as in orthochess.