The channel framework does not yet have any hooks for play/pause/stop events. I believe that if you wanted to get creative, you could have your plugin poll PMS for those events but it's not supported behaviour and could get messy.
I haven't messed with live RTMP in quite a while since PHT is the only client which (in theory) supports it. At that point in time, it was unreliable and buggy. Any improvement on that front would likely be incidental since, I don't believe that supporting live RTMP on PHT is a priority (particularly since no other Plex platforms can handle them).