i made a heat shield on one of my bikes, but the main problem is lack of room. it's a tight route for an exhaust when it's coming out the back, and a heat shield can actually make it worse, just because your leg will always be resting on it. it may not burn, but it'll be warm.
it's not exactly a design flaw, it's just what happens when you start modifying stuff.
you're right about the rack mount. matter of opinion. i see a rack as a more utilitarian option to pedaling. gets you where you're going in the simplest way possible. where as an inframe motor lends itself to customizing, modifying, and is more closely related to motorcycles.