It is not true that you can not bring models into Google Earth. Various sources have confirmed that model import via KML and I expect via the API will remain possible. Google also said that the collada format continues to be supported.
So, there is no reason your models can not be loaded into Google Earth. The only limitation is, nobody else will see them unless they load your kml file or visit your web-page containing the API code to load the models. My diorama system is based on this very principle and it will continue to function.
However, the new system looks like a continuous mesh. Ground, buildings, it is all the same surface. So you can't simply turn off the building layer. I wonder if and how Google plans to deal with that.
Maybe it will be possible to turn off the photogrametry and have SRTM elevation data instead.
Another thought is that Google might consider to keep a small selection of the very finest land-marks as a separate layer. But again, a nice token to the creators but I expect virtually nobody will ever look at it.