Are there cheeses that are not suitable for making for macaroni and cheese? I've noticed that american and gruyere are dominant cheeses recommended in mac and cheese recipes. I assume this has to do with their mild flavors and ability to melt somewhat quickly.
But what is to prevent someone from using cheeses like parmesan or blue cheese? Is there a criteria for what constitutes an optimal mac-and-cheese cheese?
I can think of three general reasons why some cheeses are better than others for melting:

Age:
The age of a cheese often determines how well it'll melt.  For instance, a 5 year old cheddar will (generally) not melt very well into a bechamel sauce.  

Texture:
You may find that stringy cheeses like mozzarella make the mac'n'cheese more difficult to eat, as it's a little impractical to have strands of cheese hanging from your spoon.  At the same time, cheeses like parmesan or feta may not melt the way you'd expect for a cheese sauce

Taste:
As for flavour .. I don't think many people would line up for macaroni and blue cheese :o