Earlier quoted context omitted.
I agree with #2. I think Microsoft is likely producing a new operating system as we speak--one that hopefully is focused on security first. Perhaps a realization of the Singularity OS is coming. OS APIs running managed code, perhaps? The future will certainly be interesting for the Windows ecosystem.
Windows as a brand is still way too big, and unlike IE its reputation is okay and its market share huge, Microsoft has more to lose than to win rebranding Windows. I don't see it happening, but IMO there's no reason why Windows can't be the new Windows eventually.
That said, I'd agree that it'd be a bad move to rebrand Windows just yet. Then again, DOS was a well-known and well-liked brand too.