The thing with native ePub support (even without DRM) is that it would be a great boon for those of us that mostly read non-DRMed/non-Amazon stuff.
While I suspect the number of stores that sell non-DRM books is shrinking, in the past week I've bought books from Baen and Fictionwise. In all three cases, the mobi/PRC files were atrociously formatted.
So I had to download the epub and convert to mobi and then put on my Kindle to see what they look like. Then load them in Sigil, tweak and convert. Repeat several times before I got it right.