Right now 50 stars is rows of 6 5 6 5 6 5 6 5 6 so make the center stripe 7.
My thought (even before seeing the Wiki version) was 51 = 17*3
Three rows of 17, or 17 rows of 3 doesn't seem balanced.
17= 8+9 so,
3 rows of 8 and 3 of 9 (alternating) results in a flag with a similar balance/look to the existing. People will hardly notice the difference. Unlike the WWII flag with 6*8 in neat rows and columns.

Next may come 52 states (cards in a pack) = 4*13. Same basis, 8 rows of 6 & 7 alternating. Or 7 rows (4 with 7, 3 with 8 alternating)