only thing I hate about the P90, like really pet peeve cannot stand, is that damn 5 inch trigger pull.
If I had to use one, I'd throw an optic based SW-comp in there and wire a button switch behind the trigger for a 3mm trigger pull. Then hack off all the extra weight, maybe increase the spring pressure a bit.
It may surprise some people, but the biggest difference in trigger response between a PTW, polarstar, and AEG, is the trigger pull.
A P* and a PTW have 1-3mm trigger pulls, but it's surprisingly slow for an AEG to make that 10mm trigger pull.