To my knowledge every watercooled VW (and most of the older Audis) can be chip tuned, or resistor tuned, or 'mechanically' tuned for fueling. Ignition can be addressed within the current rules.

They cannot all have a nice, wide process window set of optimum maps, but when I race, my motor spends most of the time at WOT and 4k + rpm, so a super wide process window is not needed. I don't worry much about how it runs in the paddock and warmup lap, as long as it keeps running and goes when the green flies.

There are some old 'chipped' CIS-E boxes floating around that a UK company was charging a fortune for, but I think they are NLA.

That said, I do think small gains could be acheived with a programable, fully mapped system. I just would not go there without being at 100% on all other aspects of the powerplant. This is the first year that I have seriously considered converting to a stock electronic injection system and taking advantage of the current rule using Megasquirt or Microsquirt in a California spec. Digifant box. However - I am still not sold on it - my current setup allows me to get the fuel right where I want it, and works well enough to win in a G Production car.