This is misleading because they're not using that word or proposing that we should rename the vagina.
The term was included on a glossary of terms that for professionals providing care to transgender people, to explain some of the terms patients might use:
https://www.jostrust.org.uk/professionals/health-professionals/nurse-gp/trans-non-binary/language
It doesn't appear anywhere else on the website. The correct word - vagina - is used throughout, for example:
https://www.jostrust.org.uk/information/cervical-screening/what-happens-during-cervical-screening
So a bit of a non-issue, really?
I personally find the term 'bonus hole' hugely offensive, and would be rightly outraged if it was ever used in an appointment. But I also think that it's important that people who identify as transgender men who have not had their cervixes removed should be supported to attend regular screenings, which are essential healthcare for all biological females who haven't had their cervixes removed.