Well, never and ever are a long time. Jeff Bezos was always jealous of the closed system Apple has/had with iTunes... so he put up his iTunes busting DRM free MP3 music store. He claimed at the time that open standards blah blah blah....
Now, he totally copied the closed iTunes/iPod system with the Kindle/Kindle Store. The have created software for the iPhone/iPod Touch, PCs and Mac on the way. I hear they are also going to support other devices to. They own the mobiepocket software which will be pretty easy to port. They also supposedly loose money on each 9.99 ebook they sell... so making up that revenue with Kindle sales and also making sure all the back catalog ebooks that they do make money on will be there.
So, all the above is the argument against them moving to ePub.
The argument for it is that pretty much every other reader device has been adopting ePub using the Adobe DRM. So, if the Kindle store did support this form they could possible sell a lot more ebooks. But, unfortunately you can't make up a loss in volume.