Windows Longhorn (Vista before the development reboot) actually shipped with SQL Server Express for WinFS. Though dotNet based shell and SQL Server Express based WinFS was too slow and consumed too much CPU resources.
WinFS was too slow and consumed too much CPU resources.
I'm genuinely curious what your source is for this. From the following uncited text on Wikipedia?
"An early revision of WinFS was also included, but very little in the way of a user interface was included, and as such it appeared to early testers to be nothing more than a service that consumed large amounts of memory and processor time."
https://en.wikipedia.org/wiki/Development_of_Windows_Vista and https://en.wikipedia.org/wiki/WinFS