Well, my bevel up planes are shoulder planes and a skew block, so this is kinda abstract. But on the face of it, it seems that Derek would want to camber his bevel-up planes on the primary bevel side, and not the back, for the reason given by Chris.
On the micro-bevel point, the highly-qualified will surely be able to manage their available clearance. My original suggestion was directed more toward those getting their start in hand planing with bevel up planes, because changes made to a blade back are hard to undo. If you have 12 degrees of gross clearance, and approx. 7 degrees of that is a working minimum, then you have 5 degrees of usable clearance, which the lower wear bevel begins to chew away at as you plane. So a 1 degree micro bevel takes 20% out of the usable fraction--the 7 degree base is fixed. And if 1 degree becomes 2 through some imprecision of technique or stropping, etc, then that's 40% of the available. This would not be noticed on the initial planing strokes, or initial 'wow' factor, but would bring about re-sharpening faster than if the back were left dead flat.
A follow-on query is whether clearance angle affects the speed at which the lower wear bevel develops. In other words, does the clearance angle that you start with affect how many feet of shavings you can put on the floor before it's time to re-sharpen? Seems like it might, because at a real low bedding angle, wear on the lower blade edge will rapidly expose more metal (and more wear). In the bevel-down world, the Japanese are very careful about honing angles and bevel-flatness for this very reason. In the bevel-up world, more data and experience will shed light on whether this is of practical concern. In this connection, Mr. Holtey bedded his No. 98 at 22.5 degrees for some reason.
Wiley ... hoping Alf doesn't punch my ticket and send me to the corner for a while.
