According to TrueAchievements (via ComicBook.com), fans who are eagerly anticipating the next adventure of the Blue Bomber will have a chance to give the 11th entry in the main series a try nearly a month early:
The Mega Man 11 Demo Version is currently listed as being available on September 4th and will allow players to "take on all kinds of enemies and traps in the Block Man stage" and "use the new Double Gear system to slow down time or power up your shots and take down that boss".
I'm listing this one as a "rumor" for the moment, as I've not seen anything from Capcom on this, and while I've seen several sites pick up the story, they all point back to TrueAchievements, and I don't know how reliable their unnamed sources are on this, so better safe than sorry.
That said, it's hardly an unreasonable expectation, as Capcom did have demos for Mega Man 9 and Mega Man 10, though those came out a bit closer to their respective release dates.
Mega Man 11 is currently slated for an October 2nd, 2018 release on Xbox One, PlayStation 4, Nintendo Switch, and Steam.