The only concern from my perspective is compatible fuel lines that won't disolve over time.

I'm sure Audi is gonna hate the idea of home-brew biodiesel or heaven forbid, homebrew veggie oil systems.

B5 for FAME-based biodiesel is still the max Audi will support. One of the big issues of homebrew is when you use too much methanol, which eats the lines. The official statement is that FAME-based biodiesel will ultimately gum up the injection components.

coming years as govt mandates requires hire percentages in road fuel, home heating oil, and offroad use.

I will be running 80% B100 with 20% WVO (heat filtered to 5 micron).

I'm just waiting for a new TDI to run on B100. I just need to be careful on quality control.

B5 if you are lucky. read over at tdiclub.com for on going experiments are 2009 Jettas with B100: 50-50 at the moment.