Kobo should only use "industry standard" rendering engines that displays all epubs regardless the vendor (Kobo, B&N or any other shop) who sold the epub.
For epub 2 that is (like it or not) Abobes RMSDK and used by almost all dedicated devices (Sony, Bookeen etc.)
For epub 3: I don't know.
Readium?
If Kobo wants to use a proprietary format it should be better than the "standard" and solve (some of) its limitations.