I can't guarantee future compatibility. Ryze could shut the door for 3rd party apps in a heartbeat. But: If they did this they'd face nasty situations where your Tello does no longer fly with your brother's phone. I doubt they want to hear all the customer complaints so I doubt they will do this.
Personally I keep one of my Tellos updated to the latest firmware, but the others stay as they are. I'd update them if I notice some improvement (which I haven't so far). Don't fix what isn't broken!