No after sales upgrades.
Toyota/Lexus hardly ever have dormant features. If a feature isn't included then the sensors aren't in place and a completely different wiring loom is used without the wiring to the sensors. The only exception that I can think of on a Lexus in the last 15 years is the retrofit of cruise control to the CT200h because the wiring is in place and the ECU has the functionality.
With regards to blind spot mirror, you would need: The glass with the indicator in it. The mirror connectors won't have space for the additional wiring, the wiring loom won't be in place from the mirror to the ECU, the mirror ECUs are different to standard with the extra functionality, the system works with microwave sensors on either side of the vehicle at the rear (behind the side of the rear bumper) so you need those as well and the wiring.