Elixir version manager for Windows?

No. Not in my point of view.
You should be able to install multiple versions from custom scoop manifest files.
And then only, as example now, rename the desired version within the scoop shims folder.
Then in a new shell the desired version should be available,
as scoop added the shims folder to windows path.

But different approuches would probably work also.
Scoop does only symlink the latest installed versions to a current link folder.
So it does not uninstall old versions automatically, as its always only a linked potable installation.