No, the grouping now works seamlessly between Google/Nest homes, HDMI Chromecasts and CCA. But you are correct that originally, that was a CCA-only feature.
Chromecast will support FLAC stream playback up to 24/96 but similarly re-samples to 48Khz. It still sounds fine to me but it would be great to see a future feature where we could toggle on/off that forced-48Khz output.
AFAIK the reason you typically see this forced 48Khz behaviour is that way...