DXVK is a windows program that thus runs on Wine also. It would make sense to include/merge it into Wine at some point, since that is its target, but AFAIK DXVK doesn't even link to anything Wine specific and it thus a completely separate codebase.
DXVK is not intended to be merged into wine. It's written in c++, and prioritizes usability over accuracy.
It isn't intended to be merged, but it is intended to be used with Wine. As such, one can envision it being provided by default with Wine.