even on the track there really are no weight advantages to a half radial rear track wheel. the length difference between a radial and a 2x lacing on the same hub and rim is ~10mm for 32h; basically over the course of the wheel you're saving less than the weight of a spoke. we're talking tens of grams— which you could more effectively save, again with the same hub and rim, by using a lightweight tube and/or tire. not only is one likely to save more weight this way, but it's also the furthest radius from the axle.

if it's that important to you to save the weight of a spoke, from the location where spokes typically exist in a wheel, it's more effective to lace up a 24/28h wheelset for track use.