Maybe add Google Street View as a button where bold, italics, and the other things are?
That would require modification of the forum software. The mods don't seem particularly interested in making custom enhancements to the software just for this forum, so it would have to be a contribution to the SMF project itself.
This is entirely possible, but would require someone with experience in PHP (like me) and working in open-source projects (not so much me) and who has a good bit of free time (not me).
Also, better than simply generating a url to a static image, theoretically a modification to the software can make it possible and easy to embed pannable, zoomable Google maps and Street View scenes, hopefully without opening the can of worms that comes with allowing arbitrary iframes.