<3.99 is "old"?? Not sure why there would need to be such recent cutoff date for any plugin. My KindleUnpack plugin (a UI interface plugin) will work from calibre v0.8.60 up to the latest Python3 betas. I understand people wanting to possibly bail on supporting the old PyQt4 versions of Sigil - that's one thing. But if your plugin worked on calibre v2.0+ (the switch to PyQt5), then it should still work on the latest (python2) releases (with no porting necessary).
Getting them to work with Python 3 is another story, but other than that, I just don't see any valid reason for a currently working plugin to drop support of calibre v2.0 - to present (python 2).
What am I missing? What drastic plugin api change happened between 2.0 and 4.11?
