Port the markup parser to Google Apps Script for use in Gmail / Google Docs. Gmail will be easier to set up and manage since the script can use plain HTML.
Gmail
Create email with todo markup
Tag email with tdx label or similar
Send email to self, copying anyone else who should see the generated markup
Script parses markup and generates an HTML file, served via GAS
Script emails link to the HTML file to original sender and anyone copied on markup email
Google Docs
Create doc with todo markup
Run script from Tools menu
Script generates a new doc with equivalent HTML markup as native Google Doc elements
Email generated doc url to anyone who has access to the original markup doc
Port the markup parser to Google Apps Script for use in Gmail / Google Docs. Gmail will be easier to set up and manage since the script can use plain HTML.
Gmail
tdxlabel or similarGoogle Docs