To retain the foldability of the screen your only option to "update" it is to fit an mmi box. And the one that most recommend is the one from Mr12volt (as already mentioned). With all of the others they all connect via the analogue AUX socket (same as any Android screen will!!) and you have to press and hold a button to activate them. With the Mr12volt it connects via the MOST fibre optic network to give you digital sound. It also integrates just like any other section on the iDrive system, ie; you just press one of the controller buttons to switch over to it. Once on the screen, which will come up straight away if that's how you left it last time, it'll display your map and music player (or whatever you've chosen) which is directly from your phone.
If you go with the Android screen then it won't fold, it's analogue audio, it's in your face all the time, there are reflection issues with the roof down (never had a reflection issue with the iDrive screen as its designed that way!).
It will display all of your original iDrive stuff though and it will do what you want from it (apart from fold).
Don't get me wrong, it don't have an issue with the screens, it's think they are good, especially for the non-iDrive systems as its a great upgrade, but for an iDrive car it would be a no for me.