I tried to fake out Google Messages, sending "Liked..." but couldn't do it. There's apparently more in the msg payload that's sent than merely the text content. I did send the same msg to the iPhone multiple times and reacted to one. Android displayed the reaction emoji in a separate msg, apparently unable to detect which msg the reaction was for. Also, image reactions don't appear to work yet. Still getting "Liked an image."
Reacting to unique text msgs does appear to work as expected. I composed multiple consecutive msgs, hitting "send" before the prior one was done sending and reacting to each one. There was a delay with the reactions showing up on Android, but they all eventually appeared on the correct msgs.
It's still not working on my P6P. Would be interested to hear if it's working for any P6 owner.