On the flipside, a radial wheel laced heads-out would have to be more aero.

No 'nope' about it.

AFAIK they're typically laced heads-in though... and I seem to remember reading an article which claimed a small aero benefit for such a wheel; I think this proposition deserves more than a single word in reply.

After all, it stands to reason that a heads-in radial wheel should create less turbulence thanks to all the spokes on each side passing through the same spot... on the other hand, plain radial spokes passing through the 12 o'clock position (where they go twice road speed) present a circular cross section, whereas plain tangential spokes present an elliptical section by virtue of their angle. An interesting question whether one effect cancels the benefit of the other, but this could be side-stepped by using elliptical or bladed spokes.