Yes, mostly waiting on platform support - Android L finally adds built-in PDF decoding support (which has been built into iOS from day one), Android 4.4 added a more capable embedded web browser module (necessary for decoding EPUBs), so once those become sufficiently dominant that we can reasonably launch a new feature that requires them we can finally add those features.
Some other formats are likely to stay iOS-only for a while, though, for example Word documents - I'm not aware of any plans to add offline Word document decoding support on Android as Apple offers on iOS (I think Google would prefer that people do all of that through Google Drive).