There have been requests forwarded to Ilford (in the "postcard paper" thread in Product Availability). The official line was that the numbers are faint to prevent "wrapper offset" in which the numbers print into the emulsion where they contact via chemical fogging or changes in sensitivity -- but we were told they'd look into printing them more strongly.
FWIW, I've found if I get a strong enough light on the red window, the numbers are easier to read, and with the center-strip window for 6x12, there shouldn't be a problem with light reflecting around the film edge to cause fogging. And the paper on all modern films except possibly Forte/Classic/Bergger and Efke is more than opaque enough to withstand direct sun exposure for limited periods.