Was going to post something similar on July 22nd, but I might as well do it now.
1.) The next main series game: Pretty much a no-brainer. We know Sonic Team has been cooking something up in the oven for awhile, we just don't now what it is. I can't predict anything other than it will star Sonic, you go fast, and collect rings.
2.) New Sonic Boom: Fire and Ice trailer: Now is about the time we get a new trailer for the game, one that hopefully convinces more people about. I also expect them to show a new cut scene.
3.) Sonic Boom season 2 announcement and sneak peak: Season 2 is pretty much all but confirmed, and it makes sense it show it off here. They'll probably explain the differences between season 2 and season 1.
4.) Sonic in LEGO Dimensions trailer: It will likely show off some gameplay of him and his level. Maybe an interview with some people at Traveler's Tales. Hopefully we'll see some more characters other than Sonic.
5.) First4Figures shows their 25th Anniversary statue: Possibly show off some more merchandise as well.
6.) Some news about the Sonic movie: We know next to nothing about the movie, so now would be a good time to spill the beans. We'll probably get a brief synopsis and what Sonic will look like. We could also get the reveal of a director and some cast, but I find that more unlikely. (This is honestly what I want to see the most, aside from the new game of course)
7.) Sonic 1 and 2 remastered get console releases, with 3 and Knuckles announced: Pretty much getting into wish-list territory, but I think this would be a great way to celebrate the classic era.
8.) More PC ports announced: Heroes, Colors, and Unleashed are some of the few main series Sonic games to have not made it to PC. With SEGA having some more pocus on PC gaming, I can see them wanting to port these games.