Sometimes I wonder what would LH would Look like from an OS point of view if it could fully innovate. If it could truely come out and say that from an OS point of view. Legacy support is not guarenteed. Dos 1.0 to 6.22 will not run in the platform except in a virtual machine.
I think with the advantages in Virtual machine technology, Microsoft can/should/might quite likely cut more and more legacy support in the OS and move forward, and indeed I believe they should. I also quite believe they consider this very heavily.
Already you see how Vista Enterprise is bundled with Virtual PC Express (although its a bit funny that Vista enterprise has VPCe as a selling point when you can easily use virtual PC full version for free and run in all Vista versions...) as a way to be able to run legacy business applications.
I think MS will be able to drop legacy support in the OS sooner than we think, at least I hope so.