If you are using Windows 10 as your primary machine, and interested in e-books, Microsoft seems to be adding e-book store in Windows 10 Store. Reported by MSPU, it’s going to be a dedicated section just like Apps, Games, Movies & TV, and Music.
While Microsoft Edge already supports EPUB format, so you will not need to buy any dedicated app for reading it, but if you do, there are many apps available for it. However, we will have to see if Microsoft actually allows it to read them through other apps, or you will launch their own app which can manage everything for the readers.
The update is expected to come with Creators Update which is scheduled to arrive this April, and it will be available for all Windows 01 powered device including those using Mobile device.