Good point. I hadn't noticed that limitation.
I think the most commonly used messages will fit in 80 bytes. The ones that don't (mainly the ones that allow for a bit of ASCII in them) should also be the ones that don't get used very often.
Actually that's a very good point, going through the spec you have defined a total of 11 different transaction types, the largest of which requires a payload of 57 bytes. 'Class C' could thus handle all (currently defined) types in a single packet & we'd only need to attach multi-sig when we need extra space.