Should IE7 and IE6 work side-by-side?

The recent revelation that the source of some of the problems with the most recent IE security update was due to people running an unsupported 'side-by-side' installation of IE7 Beta 1 got me thinking. Should IE7 be available side-by-side with IE6?

From a technical standpoint, since IE7 will only be available as a separate download for XP SP2 and Windows Server 2003 SP1, it would be possible to use the side-by-side assembly features of these operating systems to leave the version 6.0 versions in SYSTEM32, and use manifests to direct the IE 7.0 'shell' application to the side-by-side 7.0 versions. Third-party applications would then be able to opt-in to the new versions. Indeed when I heard that IE7 would only be available for XP SP2 and Server 2003 SP1, I considered whether this system feature was one of the reasons.

The benefits of this approach would be a lower risk of breaking third-party applications - indeed, also Microsoft applications which use the Web Browser component and other internet libraries - which presumably would also reduce - somewhat! - the test matrix. It would allow web developers to more easily test sites with multiple rendering engines. The downside is of course that older applications like Outlook and Outlook Express would not get the updated rendering engine, unless updates to those applications were made available.

We know that the IE team intend to keep 'quirks mode' rendering as it does currently, but that pages declared with a 'standards' doctype will use updated rendering. I presume this also applies to applications embedding a WebBrowser control. I anticipate this will have an impact on some applications no longer rendering correctly.

Explorer is an interesting issue. If a user types a URL into the address bar of Explorer with IE7 Beta 1 installed, a new browser frame is created (at least on my machine, this may be a configurable option?). This differs from the normal behaviour which is to turn the Explorer frame into an IE frame. Likewise, typing a folder name into IE7's address bar opens a new Explorer window on that folder - IE6 changes the frame to an Explorer view. We know that Explorer uses a number of the same DLLs as IE does - in effect, IE7 will also be updating a lot of Explorer's behaviour.

From the general user's point of view, will they understand having two versions of the same browser installed side-by-side? If the IE icon is on the desktop (having the classic Start menu enabled causes this to happen) which version should it point to? Is the concept of side-by-side versions of IE sensible for most users? I suppose there are two issues - whether the platform components are available side-by-side for application developers, and whether the front-end, which is what most people consider to be IE, of IE6 remains accessible to the user.

Of course it would be a chunk of work to ensure that IE 6.0 and 7.0 used the same profile information compatibly. Or, even, should they? Would users want to use different security settings between the two browsers, for example? Or set different home pages? It's already confusing enough for users to be told in some applications that changing the Web Browser options will also change their settings in IE.

I've already been told that there are no plans to go side-by-side, but I'd be interested in your thoughts.