Nest will work with some magic but is not officially supported
Sonos is supposed to work but I have never been able to get it to integrate properly. I believe they have even pulled the smartapp off of the marketplace due to the trouble they are having with the integration.
Your gen 1 sensors won’t work, but gen 2 will. I have a lot of those (motion and open/close) working great with ST. I also have several monoprice devices working great. Your Nests will work with the help of a Community developed solution, but Sonos is a different story. I suggest reading up on that. All in all I think you’ll be pleased with the change.