So let's get a few things straight: EPUB is basically stripped down HTML and CSS. Besides the clusterfuck that CSS inherently is, EPUB has its own quirks dealing with how pages are separated. Plus, there's no discernible advantage to using EPUB over PDF or CBR. EPUB was made for adaptive formatting but when you're compiling page-separated image files there's no point to that as there'd be hard page breaks anyways.
I'm really not sure where EPUB would be useful. Any ebook reader will support PDF and if you have a phone there's plenty of CBZ readers out there for whatever OS you're on.
Perfect Viewer is what I use on android.
ComicRack works well on iOS. iBooks and Google Play support PDF out of the box.
It's not that EPUB is impossible, it's simply not worth the effort when there's simpler formats for comics out there.