They can't support the Kindle format because it uses a proprietary DRM, and Amazon are not about to license their tech to a competitor. And they can’t reverse-engineer the DRM to make a compatible app because that’s illegal, as well as copyright infringement.
As far as I can tell this is impossible. If someone figures it out, please let me know.
BTW, if you ignore the DRM then the concept of a universal reading app is redundant. All you need is a cnversion program, and that's freely available (try calibre).