Aaccurate 3-d scanning of 3d environments - houses, mines you name it. I think the tech is there in your pocket and with good software plus very accurate measurement of location, orientation + panorama/spehrical photo shoots, you could have very high quality recreations of real world areas - which in turn could be explored, modified and enjoyed in VR/AR/MR.
For example simulating house refurbishment or furniture purchases, remotely inspecting places to buy/rent/go on holiday.
The tech is mostly there, but I'm too lazy to put it altogether as I know that someone with access to more capital will also attack it, sooner or later, not just startup but IKEA, Airbnb, etc...
BBC's Italy's Invisible Cities used 3D scanning to showcase areas in three Italian cities (Naples, Venice, and Florence). Seeing things mapped in 3D made a world of a difference trying to understand those spaces. It was a great show.
This is a super interesting topic to work on! There's an academic initiative which does exactly this, it's called the Digital Historical Architectural Research and Material Analysis or DHARMA [0] for short (it's at the University of Notre Dame). Figuro3D [1] is a startup (also out of Notre Dame) which borrows a lot from DHARMA and applies it to 3D printing.
The tech is mostly there, but I'm too lazy to put it altogether as I know that someone with access to more capital will also attack it, sooner or later, not just startup but IKEA, Airbnb, etc...