It looks like some people in the thread below have figured it out — we actually have this. You can start a chat both ways; the system will automatically recognize if this person is on Skype for Business or on Teams.
Thanks and let me know if you have any questions.
An error occurred while saving the commentAnonymous commented
This is still not working. If I send a message to someone who once used teams it still doesn't show in their Skype Feed.