Moving from a Megasquirt to the factory ECU I would think you'd find things a lot less "flexible" - my experience has primarily been with aftermarket gear - a couple of different Electromotives and the Autronic SM4, where the ECUs are designed to be programmable and the software already exists.
James has been doing a terrific job here, but this is definitely a work in progress - with his help I have been able to monitor quite a few of the operating parameters on my vehicle (a '98 GV) and I'm now toying with the idea of my own 'digital dash' - although for the first it'll probably only display fuel consumption.
Rhinoman pointed me here from Suzuki-Forums, after I posted a question about accessing the serial interface on my X-90 engine installed in my 89 model Suzuki Sierra.
I have previously set up a v2.2 Megasquirt on a 1.3 8v engine in the same vehicle, so have some engine management experience. I'm looking forward to learning a lot more!