Or, perhaps the craziest idea of them all: Re-open the South-East Island aka the War Island. Doing so would provide a boost just from returning old players. Off the top of my head I can think of at least 3 or 4 people who would return to BM if word got out that they could play on SEI again, and they would probably start additional characters on other islands as well. I know Tom has said that the war islands didn't fit his idea of BattleMaster, but I can only say that almost anyone I know in the game on a personal level thinks closing them was a bad idea. Myself included.
To be honest, I have been slowly coming to believe this as well.
I don't agree with all of the reasons people have given for it being a bad idea, but I do now think that they were a net benefit to the game.
If we were to do this, I think it might be worthwhile making it 1-char-per-player, but make that character free—it doesn't count against any character limits. That would mitigate, to some extent, the potential drain of characters from other continents.
