Cheers, I did send an initial mail to the dev list, but think it might have got eaten as I didn't see it (also had a bit of bad luck updating this ticket, updating the description, not leaving a comment).
One thing I found out, is that even with COLLATE NOCASE sqlites regexes don't default to case insensitive, so that would need some support at the django end.
I had a bit of a look into how the postgres citext works, but couldn't work out how to make Operators that integrate with Django in the same way.
I guess a really tiny implementation, as fields.py might be a start ?