Auto hold and hill start assist are two different things. HSA simply maintains brake pressure for a few seconds after you release the brake pedal, giving you enough time to get on the gas and move off. This is what I have fitted to my manual car and it works very effectively.
Auto hold as you describe sounds very nice, but its not fitted to my car. This is something that is unique the cars with an automatic gearbox. The application (and release) of the handbrake is totally manual with no assistance from the car - other than being an electronic switch of course. Wouldn't mind something like that, but you don't miss what you've never had........
2012 BMW X3 20d M Sport Manual - Sapphire Black/Black Leather and a 2015 BMW M4 Coupe - 6 MT in Yas Marina Blue with Full Silverstone Leather.