One of the facets of Topps cards that I prefer to Upper Deck is that they have Hero numbers. The numbers were present on the cards I grew up with and I enjoy seeing them on today's cards. Topps has also "retired" the number 7 to be used exclusively for Mickey Mantle.
If a card number can be retired to a specific player for on the field greatness, why not recognize a card number that represents social progress. I propose making card #42, Jackie Robinson's uniform number, a Hero Number. This way it is a living memorial honoring Jackie Robinson and what he represents. This is similar to the way players don uniform number 42 on Jackie Robinson day during the Major League season. Similarly I also think that Robero Clemente's 21 is worthy of the Hero number treatment as an honor to him and the rise of the Latin player.
Each year the cards could be a different player, this would surely generate some free publicity for Topps as the players and their credentials would likely be debated beyond baseball card circles. In the initial years the numbers would go to a Dodger and a Pirate but beyond that I would expand the player pool to all 30 teams. Juan Pierre would be a good pick from the Dodgers for the #42 honor. Perhaps Ian Snell, who represented Puerto Rico in the WBC could be the initial #21 representative.
In a hobby that is short on innovations that are not in reality gimmicks, I think it would be easy to do and would also generate a significant goodwill return for Topps.