I'm pretty sure that MA-xxx is pronounced just fine when used on a ramp. For example, this:
https://www.waze.com/editor/?env=usa&lo ... s=71334796
is pronounced "to EYE-95 north, Massachusetts 128 north, Massachusetts 30, New Hampshire, Maine". Is the pronunciation different when used on another kind of road segment?
Anyway, I like the MA-xxx convention but if Waze isn't going to play ball and make this pronounced according to local customs, then I guess SR-xxx is as good as anything else. The usage of the term "Route" when referring to a state highway is so pervasive and consistent around here that anything else will be unintelligible to most drivers. At least "state route" has the word "route" in it so some people may understand. However, I think many people don't even realize that what they call a "route" is actually a state road, so the leading "state" is still likely to confuse them.