So, I can add ANY gauge? I think I'll add a turbo boost gauge. So I need a turbo [...][/b]
Illogical argument. Adding a turbo is an illegal function, whereas adding an aftermarket ECU is not. What you are describing is using one unrestricted mod to justify an illegal mod. Obviously not legal. However, using one unrestricted mod to assist another unrestricted mod does not mean that its use is illegal (assuming of course it's not further restricted).

It is in fact allowed, 'cause once something's unrestricted, it's unrestricted.

I know that traction control is a non-legal function...[/b]
Whoa, whoa, chief: where is traction control made non-legal? ECUs are currently unrestricted insofar as what you can do inside the stock ECU housing with the stock wiring harness/sensors; where does one now assume that the functions of that completely-legal device are further restricted? Engine management systems are wide open (current restrictions noted); outside of that you can do whatever you want.

So, you're calling it a "prohibited function"? Well, the purpose of an ECU is to Electronically Control the engine, and that's exactly what it's doing with traction control. Are you implying that we're going to get into exactly how the heretofore unrestricted ECUs actually do their work? Are we going to list for each vehicle exactly what functions each OE ECU does and limit it to that? Or are we going to simply allow someone to do with it whatever they can, under strict specified physical limitations?

We may not WANT traction control, but it's way legal. Remember, "if it says you can, you bloody well can!"

Aside from the fact how TOTALLY impossible this would be to enforce...

...they are no longer guages, they are ecu inputs.[/b]
I agree, Evan, which is why my scenario relates not to now, but to the proposal to allow other inputs with an open ECU.