/jp/ didn't work because /jp/ was trying to quarantine too much. You'd need an ENTIRE BOARD to effectively quarantine Touhou. Putting Touhou and ALL Japanese culture on one board is like putting MLP and all little-kid-show cartoons on one board. Of course the Touhou posters, who loved 2D 2hus, hated sharing a board with people who loved 3DPD trash. If moot would have just given them the /th/ - Touhou and /ota/ - Otaku split they all wanted and made /th/ an off-topic board similar to [s4s] but Touhou themed, everyone would have been satisfied.
/mlp/ has worked exceptionally well.