a 7-8" Android to show functions such as Lambda, Turbo, oil temperature etc from ECU is doable
It's as if you had hacked my computer and knew what I've been doing today.
A similar gauge display function is available with MegaSquirt (MS) ECUs as well. And today I have been reading about the requirements and limitations for it. The displays are not nearly as complex as the one in the video though...that is a very elaborate custom system.
The MS ECUs use TunerStudio (TS) software. And TS has the option to display the gauge screens that you would see on a laptop, but on a Android tablet. Lots of options on what is displayed and how it looks. Like you described BlueTooth (BT) can be used to connect it, although some MS ECU's will require a BT adapter because not all models include it onboard. I believe you can also connect it with a USB cable, eliminating the need for a BT adapter on those models. But I'm noticing most tablets only have one USB connection, so you would not be able to power the tablet with the car's charging system and connect to data on the ECU at the same time (I'm pretty sure the ECU's USB doesn't include a power output). And if the tablet is being installed in the dash as your gauge display then I would not want to run it on just the internal battery.
In addition to having BT, the tablet needs a real/full version of Android, which some of the lesser priced ones don't. Likewise it will need reasonable operating power, and memory if you want to use it's datalogging capability (another cool feature with it), that you might not get with "cheap" tablets. The people using this display feature on MS ECU's have discovered this also prevents the use of Android based head units offered by some stereo makers. So I was searching around to see what Android tablets might be good choices without breaking the bank. Afterall if I intend to leave it hardwired in the car as my permanent dashboard, then I really don't want to use a expensive high-end tablet.
There seem to be a couple good tablet choices around the $150 mark. But frankly for my low budget build that is a little high, especially when I can use reliable traditional gauges for significantly less than that. There might be a couple of less expensive tablets that are good enough and have all the right capabilities for around $80 (on sale). That is more in line with what I'd consider. Unfortunately there doesn't seem to be anything less expensive that will work for this. However this would be the last thing I'd add to my project - after getting the car restored, turbo package completely built, ECU fully tuned, and everything sorted. So it may be quite some time, and there may be better tablet options available by then.
I'll be interested to hear what you find on it.