MDLSITE-6109 it was decided that Moodle 3.9.x will be the last branch actively supporting IE11, with Moodle 3.10.x explicitly (actively) not supporting it.
One of the measures commented in that issue was the possibility of start warning users still using that browser. There are various aspects to decide:
- Make it opt-in (default off) or opt-out (default on).
- Audience (every user vs only admins).
- Store results (to avoid repeated messages, to account # of users...).
- Branches to implement it (only 3.9 or also 3.10 and up...)
So this issue is about to decide if it's worth creating such warning system, and if decided to proceed, implement it.