Last I checked, what was available of Readium was mostly useless, and depended on you having a full-fledged web engine (i.e., WebKit/Blink, or a platform-provided simile), which, err, nope, not gonna happen.
And, the nail on the coffin, it had iffy to non-existent straight Linux support (i.e., not Android).
Note that we (and by we I mean @poire-z
) maintain a CRe fork, and @poire-z has done some amazing work on it the past couple years.