On Sat, 20 Feb 2021 12:21:19 +0000, J. P. Gilliver (John) wrote:

Why would anyone want such a thing?

Collectors and researchers, mostly.

(I thought Microsoft timebombed all betas since before 7,
such that they wouldn't work after a certain date - usually less than a
year after their release.)

Those are public betas - whether its availability is limited or not. Vienna
is internal/private build. A prototype. A phase before public testing.