I thought this was a wink and a nod to just using standard latitude/longitude. Doesn't lat/long naturally solve each of your bullet points?

•Length-optimized. More digits = more precision, check.

•Precision optimized. Except for adding zeros, check.

•Precision-focused. Sig figs cover this.

•Logic-optimized. Adding or subtracting to lat or long respectively.

•Spheroid-optimized. I believe this applies to latitude and longitude, as well, since there's less surface area for a given coordinate space. Though, maybe it's the reverse, that it's more precise at the poles.