Also... check out the Sigil Plugins! thread for ideas about "incorporating" external script functionality via the "Open with" feature of Sigil.
The process may be a tad unweildy for those having little experience with terminals, batch/bash scripts, and scripting languages (like python) in general. But it's still beats waiting for "official" functionality that may never come (that's not meant disparagingly towards Sigil in any way).
https://www.mobileread.com/forums/sho...d.php?t=219835