They've had girls in the 6th form since 2011 (who had their own choir, as well as being able to join the chamber choir). There are so many different singing ensembles, I don't see why the TBC should be changed.
The school seem to have a very good plan to instigate the change gradually. My DD was one of about 40 girls in a year group of around 150 in the 6th form.
I'm not sure how many girls will be brave enough to be one of the 24 Y6 girls starting in 2027!
Trinity - going co-ed and the FAQs