Microsoft Edge Browser will be able to natively read EPUB and supports a range of font size and text size accessibility features, as well as being able to use its bookmark feature in eBooks. Edge will also get a dedicated section to reference eBooks purchased. In theory, it should allow one to read one's library on any device attached to a Microsoft Account.
Most eBooks are sold via Amazon Kindle (which also runs on Windows) and the Association of Authors agents has stated that “A lot of business goes through one retailer, so it is always very helpful to have others offering eBooks. As long as it keeps the value of a book it is welcome.”
The big issue will be the range of titles and if Microsoft can negotiate global distribution agreements with enough book distributors. Microsoft will use the EPUB feature for its technical publications.