Or even better, you could use
Jellby's Prince XML script to convert your ePub to a PDF that has automatic hyphenation at line endings, and whatever font, font-size, etc., you want it to have.
It would definitely be great to have that level of typography for ePub renderers without conversion or CSS editing, however. There's really so excuse. The TeX line breaking algorithm is open source, and more than 20 years old. If computers at that time could handle it, these devices should be able to as well.