There was a brief discussion about it on the Cabin Restyling thread. I've also been tracking it in the wiki on the fleet guide thread which is now buried. I have now added a section to the bottom of the wiki for a cabin refresh tracker by tail number.
Only three have been done so far, and the rest are on hold right now because they're testing the Phase 2 Rockwell Collins interior. A brand new plane, an A321, N999JQ was sent to LCQ for a test fitting last week. Eventually, A321s will be delivered with the Phase 2 interior, and all A320 refreshes will get the Phase 2 interior instead of the current Phase 1/A321 interior.

The ones with the cabin refresh are the following:

N568JB
N570JB
N646JB