The problem with sentry mode on the Tesla’s is that it is an afterthought and requires the car’s main computer to be operational to run the cameras which consumes 300 W of power. Not such an issue with a massive EV battery but Lexus couldn’t do the same with a tiny 12 v aux battery, or even the low capacity hybrid traction battery. Therefore it would only be useful when the vehicle was in use, not when parked up.
Architecturally there as a massive difference between a Tesla and mainstream vehicles which would make implementing the same solution difficult. The Lexus is a collection of different systems, mainly designed by different OEMs, that don’t share information between each other. It would be difficult to get the video used by one system and reuse it for something else. Certainly not with just a simple software update.