Is it possible to re-create a "warp" compatible image once any firmware changes are made? This would give people the best of both worlds (customizable and quicker boot times.)
Also, what version of android are the NEX units running? I'm wondering if xposed framework could be made to work with it... That should allow some quick changes (like bypassing the boot up "warning" screen) fairly easily.
Some ideas of what to do...
* (As mentioned,) bypass the bootup warning screen
* some digging into whatever launcher code they are using -- or just replacing the launcher (else adding anything would be pointless)
* If the device/kernel can handle multiple BT connections at once, perhaps OBDII software (such as torque) on the HU would be nice.
* getting some form of adb working would be extremely helpful. Otherwise, testing stuff will be a PITA. (However, I doubt the USB ports on the HU will work in that mode.)
* if getting adb working isn't an option, perhaps a version of the firmware could be put together that would work on a tablet (nexus 7?) to use for testing/debugging.
... just some random thoughts.