I got my toes wet merging 3.0.69 into Garwynn's community kernel and figuring out how to build a Perseus package that didn't break STweaks.
I am currently trying to get a kernel to compile with netfilter and RNDIS. My issue is this: drivers/usb/gadget/gadget_gbhc looks like a murder scene. It looks like a major project to clean it up to the point that it would would work.
Fixing it also may be a waste of time, as the android mainlining project's target completion date is coming right up.
On the other hand, as of this morning they hadn't mainlined RNDIS yet, and the clock is ticking for Android 5- so who knows if this will even be working for Android 5 (or whether Android 5 will be Linux 3.9, though rumors say yes).
Has anyone already fought with this and got it working? I am torn between not wanting to walk away from a challenge, and knowing that it's a waste of (lots of) time. :)