I looked into this as well and went a different route. I found that it was pretty difficult to get everything working the way I would like it. I mean, if you have a tablet, you might as well have that control audio too right? But they don't work very well for integrating into car audio. Then I thought, heck, what if I find a head unit that can run anything I'd like? At that point I looked into Car Pc's and E3io in particular.
In the end, I went with Dakota Digital gauges and I decided I didn't want to spend that much on a E3iO car pc and went with an android powered head unit from China instead. That's right, an actual android head unit. Basically a tablet connected to a double din radio.
I'm still working on my custom center console. That's where the new double din headunit will live. I can run my OBD2 adapter via usb or bluetooth to the head unit to display extra gauges there or run any other android dash software like dashcommand. It can also do anything a tablet can do and anything a radio can do. I'll have a reverse camera and a front DVR camera as well when I'm done, all integrated.
This is the one I bought:
http://www.autopumpkin.com/car-dvd-p...-free-mic.html
Anyway, it received it within a week and have been bench testing it. So far it's great for the price. I've got one of the micro SD slots filled with a 64gb card and as much music as I can stuff on that. When I get it installed in the car completely I'll have to see how it works but I think it will be really good.
If you went with something like e3i0's offering, you could put HPtuners right in it and never need an extra computer to tune your car. You can also get the touchscreen separate from the computer so you could actually install the screen in your dash if you'd like.
Later (supposedly this year) Parrot is coming out with their latest android head unit (Parrot RNB6) that's supposed to be the bomb.....but after it's appearance at the consumer electronics show it's been vapor ware.