I made a snap a while back of Calibre, but never published it. It’s certainly possible. The thing about Calibre is it’s a one-of-a-kind “best in class” cross-platform application, like Google Chrome (don’t hate me), or OBS Studio. These applications get tons of installs on Windows, because they’re the best/only gig in town. As such, the Linux market share for that application is proportionally very low, because the Windows user base is so very high. It’s an application which transcends nerds (unlike OBS) to normals (like Chrome). I know very un-technical people who use Calibre, because it’s the thing everyone recommends when you have an ebook reader. Less so these days where most people just bought a kindle and don’t care about freedom though.
So yeah, if someone wants to work on it, go for it. 