I think it's fair to hope for a more customizable Chromium, since customizability is one of the things Opera was known for. For me personally, things like a bookmarks sidebar and more flexible tab positioning would help tempt me to switch back to Opera from Firefox.
Well there are 2 features I really miss in Chromium (which are implemented in Opera now):
* easily Add/remove websites from the speeddial
* closing the last tab won't quit the browser (this annoyed me the most)
The saddest part about that is that opera was the first browser I knew of that allowed changing the default search engine in the first place, about 13 years ago.
Yet the old Opera was (and is) much faster than chrome/firefox. User confusion is valid if those are the users you are after. For the "what is Internet?" crowd there's Chrome already, and I think there's enough space for something else.
As I understand it all browsers on iOS use UIWebView rather than their own engines. However, the Opera Coast browser on iOS has a great user interface that is different from Safari.