Tapping into diagnostics that's already there is a good idea, but another phone on a cradle isn't so good? Perhaps somebody can confirm this:
If you have an Android head unit, could you get realtime diagnostics on a BlueTooth link to it, whilst still being able to switch away to radio, music, satnav or phone?
Unless you have and want to keep Dynaudio, an Android based head unit is more advanced and should far exceed features you will get with a genuine V.W head unit. You are not locked into expensive V.W map updates either.