Sounds like a good solution. It would be great to see that code, thanks!
Security and privacy
HTTP to HTTPS converter for external content
Our script is here: https://github.com/enovation/moodle-url_change . If you decide to do Moodle admin tool for 2.8 it may be worth moving some code into a shared library to share the code - as we will definitely want to use it across all Moodle versions.