Isn't being cross-platform, relatively modern-looking and open source already setting it apart from the current offerings?

There's great ones (like Foliate or Moon+) which are limited to one platform, there's ones that are cross-platform, but look so dated that I couldn't seriously use them for reading (like the one integrated in Calibre), and there's ones which are both fairly modern-looking and cross-platform, but not open source (like FBReader).

If this one syncs my books, reading positions, and highlights across my devices, that's gonna be a huge win in my book.