I nearly pulled the trigger on a nexus 7 last night for just this reason, but I'm still tossing up between that and running my old carputer.
Either way I'm ditching the dynavin.
The way I was planning to do it was trunk mounting a headunit that has the capability to have dual bluetooth connections and work with e46 steering controls. Streaming audio from the tablet to the HU which will allow volume control and track skip via swc and then also have my phone also connect to the HU bluetooth so I don't lose handsfree capability.
Tie it all together with an app called tablet talk so I can make and receive calls via the tablet screen.
The only drawback is that I would need to have a trunk mounted wifi router with NAS so I could have a decent amount of storage for the tablet, puts the carputer slightly ahead at the moment.
Still weighting up my options....