Apologies for the late reply, this came through when I was AWK.
Iris exports to a JSON Object Scene compatible format 4, but you are right, we only use Geometry. Switching to BufferGeometry has been a task I’ve wanted to undertake for a while, but have not come around to it. Here is a link to the issue in case you want to track the progress.
At the moment though, I’m going through a code refactor so that the part of Iris that converts Rhino objects to JSON can be used by other projects, so changing over to BufferGeometry is not high on my list until that gets sorted.