Im interested in building an ICF in ground pool here in southern CA. I have down lots of searching and can only seem to find one design firm out of AZ and most discussions are at least a couple years old. Does anyone have any current experience with ICF pools?

Any experienced ICF installer should be able to handle it. A design, with installers input, would be a good place to start. BuildBlock has the best ICFs for pools. https://buildblock.com/how-to-build-an-icf-home/icf-swimming-pools/

is anyone actually realizing any positive return over gunnite? Is there that much better thermal efficiency is the build easier etc? I live in Southern CA so fairly stable climate however we do have earthquake considerations.

ICF pools generally have better temperature maintenance than a straight concrete or gunnite pool.
As such, your power bills for a heated pool should be lower. This can also help stretch the season you can keep the pool open in.