I just use plaintext markup and text2tags to output xhtml. I have a little wiki-like app for keeping it all together and providing a Kate kpart based interface. Might release it in the future, it's pretty similar to old Sigil in some ways.
A few modifications to the markup and generation to make things nicer. Output is pretty much just thrown into Sigil to be compiled into an epub, very little editing needs to be done unless different styles need to be applied