I know there’s PonyVRVille, but Vive support is very alpha. There’s also pony viewer, which is very basic.
There is another VR pony experience, which has good support for Vive and actually contains interactive ponies, but it’s… not quite what I was looking for.
Someone should take that engine and make a proper all-ages pony interaction game though. If only I were less lazy…
Also, Twilight! Get out of the playing zone, before someone gets hurt!