I used to handle turbo ignition timing exclusively with the MSD box + a MAP sensor. This actually worked fairly well but I'm sure was a bit laggy compared to a crank & cam wheel.
I tried to see if a similar thing would work with Megasquirt. The ideas is to set the ignition map to a static value across the board, adjust the distributor until base timing is correct, then use the 100Kpa+ areas on the ignition map to retard timing. I sent some emails and the answer was "maybe" but it sounded like there were some questions about sync with an ever-changing RPM signal.
I would assume so. A single cam wheel with an asymmetrical pattern and adequate resolution could probably do it but I have no experience there.
It really probably isn't worth the effort to convert an existing batch firesetup to SFI. I'm sure injectors / spray patterns play in to the value equation as well. I happened to get lucky with experimentation and find 30lb injectors that fit the K-Jetronic heads and bullseye the intake valve with a nice fanned spray of fuel. Under these conditions I'm thinking there is an opportunity to capitalize on injector timing and keep fuel as atomized as possible. On a map that is very quick to jump rich under load I was still able to get about 25MPG at an 80MPH average speed with the AC running.