So say that MS do this...
Say their Internet Connection wizard connects to MS to download a list of browsers and then it opens a wizard to give you the choice of browser (i.e. each browser's icon with its name underneath and a bit of blurb selling the snakeoil) followed by an invitation to click on a browser you want to use. It then downloads the browser installer from MS, Mozilla, Opera, Apple, Google, or whoever, runs it, runs the browser itself, and brings up the home page.
It has to be done like this otherwise MS can get shafted from another browser provider when they go bleating to the EU, and it's easy enough to do because the MSHTML and MSXML DLLs will have to be on the system anyway.
So how would the uninitiated user know to click on the red O instead of the blue e? Everyone knows what the blue e does. And the blurb would be something like "Windows Internet Explorer is the standard browser that was built into Windows 95, 98, Me, NT, 2000, XP, and Vista" just to hammer the point home. And the uninitiated user will willingly press the mouse button over the blue e to remove all doubt and the browser they know and love will appear about a nanosecond later as it's all built in anyway.
So I'm not too sure that Opera's usage is going to skyrocket.
And what about those broadband connections that need a browser to configure them in the first place? Getting an offline installation from another computer will be close to an insurmountable task.
And then we need to wait for a complaint to the EU over the order of browsers in the list...