Status update: I just got the smdk4210 kernel booting. This is the 3.0.y-based kernel that the Galaxy S2 people are using. locerra made the necessary changes in the kernel for our tabs to boot this, and I've just done a test build for P6200. It works:
The kernel we were using before was the 2.6.36-based kernel from Samsung's GPL source release. I believe the future is for us to stick to a kernel which is closer to other Samsung Exynos 4210 devices (and more ICS devices in general).
I've only had a brief look around, but I can see that the momentary "blanking" on screen rotation is fixed. Sensors still more or less work (like they more or less did before!). Telephony isn't working, not sure why. Sound is working nicely. Brightness controls are a bit b0rked cuz we didn't update our lights library (Torch works, though).