If this was 1993, I'm pretty sure someone's head would explode at retail.
http://www.nintendoworldreport.com/news/64632/sonic-superstars-going-head-to-head-with-super-mario-wonder-frontiers-receiving-update
It's Sonic's 30th anniversary, and Sega is paying tribute to Logan's Run with it.
During the GamesCom Opening Night Live show, Sonic Superstars - the side-scrolling 4 player co-op Sonic game announced this summer - was confirmed for launch on October 17. This puts it squarely in the sights of Super Mario Bros. Wonder, which launches on the following Friday. Drop-in-and-out local co-op as well as a battle mode (4 players local, 8 online) was also shown.
A content update for the embattled Sonic Frontiers will launch on September 28, including new stages and the ability to play as Tails, Knuckles, and Amy Rose.