As if by magic, up I pop :rofl:
Yes it's possible to have a retrofitted reversing camera, and you have a couple of options....
1, As above fit an MMI box to your current iDrive, this will also give you full Apple CarPlay/Android Auto from your phone. You then simply connect and run a suitable reversing camera to this. All plug-n-play, so no coding required.
This is the screen view you'll have (you can have it in full screen, but the sensor view will be over the right side of the image)

My videos on how to fit an MMI box...
Chinese standard box.. https://www.youtube.com/watch?v=jY-pSPUz0IU&t
And the Mr12volt digital MMI box.. https://www.youtube.com/watch?v=EY4XAzUYiXk
2, You could replace the folding screen with an Android Touchscreen. Again this is all plug-n-play and gives you a host of applications additional to what you currently have (music, nav etc)
Please note this was with aftermarket reversing sensors, prior to me retrofitting OEM PDC, so may look slightly different)

My video on how to fit an Android screen... https://www.youtube.com/watch?v=VC9VFJBDFQM&t
3, For the purists amongst us, you can retrofit a reversing camera into the original iDrive. Although it was never an option on the E89 it can be done with the aid of an aftermarket emulator box and a bit of coding. The proviso though is that you must have OEM PDC already installed.
This is my current set-up, even though I do have the Mr12volt MMI box installed, I just like the OEM look of it
I currently don't have a video on this install just yet, I'll get around to this later in the year.
Hope that helps
EDIT** There is a 4th option (well 3.5 actually :rofl: )
You can go full OEM with this method...
https://www.m3post.com/forums/showthread.php?t=1720680
Well as "full OEM" goes anyway.
On my OEM photo above you'll see 5 "buttons" on the left of the image, in my version with the aftermarket emulator they don't do anything, but with this method, linked above, they should be all functional, including reversing direction bars on the image.
