Modern jerseys are made so tight in the sleeves now that there is physically no room for both piping and numbers on the sleeves.
The only striping that can go on a sleeve with numbers is on the very end of the sleeve, or the "cuff" of the sleeve, like the blue and white cuff on the current home uni sleeves.
If you were to put numbers directly on top of piping on modern jerseys, the number would have to be placed directly over the shoulder stitch, and I don't think jersey manufacturing equipment can do that. I don't think the NFL would want that, either.
One way to put both numbers and piping on the sleeves - go back to 3/4 length sleeves, over the elbow. That would really be old school.