It really is very simple for virtual tours to be added, if Airbnb dont want to link out from thir site then the just have to allow users to embed an iframe. If they havent allowed it, I would guess that it is because they want to protect the market for themselves
They appear to be up to something with matterport but unfortunatley I dont think it will be of much benefit to anybody for some time yet, Matterport's niche equipment is very expensive and - while the results are very good - it is possible to create immersive, VR tours for a fraction of the price and effort. I think that majority of airbnb advertisers would pay £100-£150 for a Vr tour which improved their chances of getting a booking. As versitile sperical cameras, (which have loads of uses beyond virtual tours) become reaily available many people will be able to create the tours themselves or at least take the photos and send them to somebody to link them together into a tour. VR could, right now, become an easily accessible and affordable tool for all Airbnb users.
Only the very expensive properties which happen to be within range of someone with a Matterport setup will pay the many many hundreds of £ needed to create a tour, so if they just stick with that option VR will only be a tool for the Airbnb elite until such a time as matterport's technology drops in price.