I agree with preferring the opt-out by default. My initial reaction to any opt-in default is to opt-out immediately and worry about why later if at all.
To further anonymize the data and increase user comfort, cycle the selected users daily so the same user's telemetry is not collected multiple days in a row. That limiting of data collection may also make it more acceptable to some users. For example, it may be more acceptable if telemetry data were collected no more frequently than one day per month or one day per two weeks.
To further anonymize the data and increase user comfort, cycle the selected users daily so the same user's telemetry is not collected multiple days in a row. That limiting of data collection may also make it more acceptable to some users. For example, it may be more acceptable if telemetry data were collected no more frequently than one day per month or one day per two weeks.