Disney announced that it's bi-annual convention D23 Expo will be presented July 14 to 16, 2017 in Anaheim, California. That scheduling puts it less than a week before the expected dates of the 2017 Comic-Con International: San Diego. Although not confirmed to be SDCC, an unnamed four-day "convention with trade show" of 130,0000 attendees as been scheduled at the San Diego Convention Center for July 20 through 27, 2017; the same description given to this year's convention.
In it's past two events, the D23 Expo has hosted significant movie announcements from Marvel Studios, Pixar, Lucasfilm, as well as it's own live-action and animated studios. The 2015 SDCC had a much smaller footprint of Marvel Studios' appearances and announcements, although the studio didn't publicly comment if it had done so in favor of D23.
Disney's D23 Expo has been held in mid-August for the past six years, making the new July dates a marked move ahead. Attendance for 2015's D23 Expo is unknown, but the smaller 2013 convention had an announced 45,000 attendees.