Extension forces HTML delivery format

[living180]

I intentionally use auto-detect as my delivery format to send messages as plain text when possible (Options > Delivery Format > Auto-Detect from a compose window). However, after BiDi Mail UI is enabled, the delivery format gets forced to HTML, which causes problems for me when sending to mailing lists which refuse HTML messages. I can still manually select Plain Text Only, but I have to remember to do this for every message.

Is it technically possible to implement this extension without forcing HTML format?