Funnily enough I was just making a list of VR tools that allow user-generated content (excluding music). I got this far:

Sansar

Modbox

Anyland

Tvori

Diorama Worlds

StageX

Google Blocks

High Fidelity

Tilt Brush

Medium

Quill

Rodin

MakeVR

Metaverse Construction Kit

3DSunshine

Country of One

VR Home

MyDream

Shape Lab

- I'm working on a feature matrix but rest-assured several of those are mature, well-suppoted and by smaller developers.