I'm not particularly keen to go through the GSOC process. I tend to find the amount of work involved in mentoring someone rather more than the amount of work it would take for me to implement the feature myself.
Generally, if anyone wishes to participate in the development of calibre, they are welcome to do so directly --
https://manual.calibre-ebook.com/develop.html
That said, if there is somebody keen to work on calibre, and they have an idea about what they want to work on, I am happy to go through the GSOC process.