I don't know why variant chess isn't more popular. For on-line games, I think it might be growing at least a little. One thing I think it needs is some Superstars - players who have a reputation for being formidable, at least in a class of games.
From my experience Evert823 is a very skilled player, and I've had trouble beating him in many games. Cobra91 also impressed me, especially when he beat me in infinite-chess, and Kosintsev is showing himself to be very skilled in Waterloo. And obviously McGoohan is extremelly perceptive, giving me fits in an infinite-chess variant with crazy-strong pieces.
Also from an active tournament, JunyJunebug and Friedmelon have shown their mettle, and are now in a Championship Game - one or both may be rising stars.
Once we have our Stars - the Pelé of football, the Muhammad Ali of boxing, or the Babe Ruth of baseball, I think variant chess will become way more exciting!
If I neglected or forgot to mention any notable players, feel free to throw in your comments. It's only opinion now - but I believe soon we will have our "Champions".
Sorry to bump this super, super old thread, but I had to bring this up again. Predictions have come true 
Here are some variants that are cool:
#1. When u capture pieces, they are not removed from the board, but relocated to any vacant square of the player's choice (bishops on the same color as originally captured on).
#2. A player's move consists of 1 move of one of his pieces, AND 1 move of one of his opponent's pieces.
#3. The game begins with an empty board, and players take turns placing, or moving pieces already on the board.
#4. As you move a piece, it is converted into the next more powerful piece: P-N/B-R-Q.
#5. The board starts in the upside down position, white pieces on black's squares and vice versa, all pawns 1 square away from promoting.