I'm guessing that as long as ePUB continues to be widely used, there will be a market for inexpensive readers for people who prefer to not be tied into a proprietary format and want the freedom to look for competitive prices. Whether there is a market for more fully featured non-proprietary ePub readers (with features like the Kindle) remains to be seen.
I have Kobo, which is 58% owned by Chapters-Indigo, a very big player in Canada. Last quarter they spun Kobo off (used to be Shortcovers) and took on other investors, internationally (Indigo, Borders, Australia's REDgroup Retail and China's Cheung Kong Holdings). Chapters-Indigo had to "go big or go home". They are not big enough internationally to be successful with a proprietary format and they sure did not want their Canadian customers deserting them for Amazon, which recently won a big court case allowing them to have their own warehousing in Canada (a first for a foreign owned book biz).
I love my Kobo, but if it were to disappear, I'd be OK with another reader that supported ePUB files, using Adobe ADE and with the ability to sideload with software like Calibre. Will Kindle make this possible some day? Mebbe. Will Google books be a factor going forward? Mebbe.
Let's not forget, we're at the beginning of this ride.
PS: Interesting article from July 10 on Kobo:
http://in.reuters.com/article/idINIndia-50020720100709