Thanks for the responses. I'm glad to hear that most people are in favor of this idea.
RabbitJockey, I think you're missing the point. It may seem like reinventing the wheel, but it's really not. It's more like simplifying the wheel.
The idea is NOT to retrofit existing TDIs with a stand-alone ECU. This stand-alone ECU would be to "repower" vehicles/boats/generators that don't currently have them.
Consider why the IDI forum on this website has 10X more posts than the TDI forums, despite the fact that there are 100 times more TDIs on the roads and in the junk yards. It's not because IDIs are more abundant than TDIs. It's not because they're more powerful. It's not because they're more fuel efficient. It's not because they're more robust. And it's really not because they're cheaper (at least, not anymore). The reason is because IDIs are simpler to swap, maintain, repair, and run than TDIs.
And why? Because they don't have all of that electronic baggage that a TDI has. For the most part, there's only 1 wire needed to make an IDI run. The same cannot be said for TDIs.
In terms of cost to swap a TDI (just from the electronics standpoint), the factory ECU and complete wiring harness in good condition are going to cost you $500. A custom harness if you need one starts at about $600. Then there's the VAGCOM tools and expertise you need to sync the ECU to the instrument cluster, and to the ignition key immobilizer, and even to the CR injectors themselves! And then if you need a "custom tune" to remove EGR or immobilizer or whatnot, or to add power, you're talking at least another $500. So you're basically at $1000 to $2000 just in electronics. And this is to say nothing about retrofitting that lovely Drive-By-Wire pedal.
I'll I'm suggesting is creating a simple stand-alone ECU to run the newer TDI engines - probably PD and CR. It would get rid of all of the extra TDI electronics baggage - MAF sensor, IAT sensor, O2 sensor, fuel temp sensor, DBW pedal, EGR, VAGCOM, OBD2, electronic instrument cluster, immobilizer/key sensor, DPF/Urea injection, exhaust side flap, intake anti-shudder flap, etc.
All of this stuff would be replaced with a much simpler stand-alone ECU that handles basic fueling and ignition timing functions. I envision boost control would be handled by a separate system, in much the same way that a mechanical wastegate controls boost independent of what the VE fuel injection pump is set up to do. Same with the glowplugs - a separate system dedicated to handling the GPs without much consideration for what the rest of the system is doing. A run of the mill GP relay might even suffice.
And as far as price points - Unless there's something I just haven't considered, I'm thinking the stand-alone ECU would be in the $500 range.