My guess: Since your 2015 is HW1 that only use the single front camera and does not use the rearview camera and it does not have other surrounding cameras, I guess no Sentry Mode and no Rearview Camera recording make sense.
Your HW1 rearview camera is dedicated to human use and none for the Automation system at all.
@tranzndance, is absolutely correct. Frankly you can not have too much dash cam/security cam coverage. I've got access to Teslacam, Sentry and also already had two Blackvue DR900-2C and give me 360 degree coverage.
I can 100% confirm that MCU1 upgrade to MCU2 itself does not give you Sentry features if you don't already have the feature or the hardware. I upgraded my 2015 S70D recently. Only additional entertainment features like Netflix and my original missing 4GLTE is included. And you will loose FM and Sirius radio features. To me, the upgrade is worth it because the new MCU performs much smoother and faster.
Hi sorry for delayed response. I haven't installed dash cam. But have upgraded to MCU2, which is just fantastic. Make the car feel like new again. Very quick rendering and instantaneous response from spotify, netflix etc.