Sorry for the late response on this one. Yes, you can currently export sidescan mosaics as a Google Earth superoverlay, which does exactly what you describe; multi-scale versions of the mosaic image, split into regions which can be loaded on demand. These can also be hosted on a server easily, with just the top-level kml file (which is very small) being distributed to the end user.
It is not currently possible to export map project images as superoverlays, but perhaps this is something we should implement.