I've a 27" bike converted to 650A. Tire choices are pretty slim for 650A though, and the bike has a little bit higher chance of pedal strike now. Fenders and fatter tires is awesome though.
Another good option is building a drop bar conversion of a vintage 26" MTB.
I totally agree that it's stupid how much racing aesthetics influence bicycle design. A bike with more clearance for fenders and fat tires as an option is only losing a hair of aerodynamic advantage.