1. "reasonable" is going to be different for every person. In this case it seems that the accepted "reasonable" telemetry to be on by default is None.
2. There will always be group of people who will never accept any level of telemetry.
In my opinion, the best approach to telemetry is to ask on first use. Explain clearly what telemetry you are sending and why. If this ever changes on a future update you ask again.