I think the 11-inch MBA is already small and thin enough
Already small and thin enough for what?
We all have differing ideas on what constitutes mobile. You also wrote that if the MBA were any smaller then your eyes and hands would be affected. Well that supports my point that the MBA IMHO still has not sacrificed enough to be Apples mobile computer. I would prefer to have the screen cramped and the keyboard puny all to enhance mobility. This is not intended for me to be a normal typical use computer.
My MBP 17 is a fine portable computer, but I need an ultra mobile computer, to take with me virtually everywhere I go. An iPad doesn't run OS X.