Google I/O 2017 is literally just around the corner as it starts next week from May 17th through the 19th, and while it's impossible to know for sure what Google has planned for the Keynote speech, it is possible to speculate on what they might have to show off or announce during the hour and half long portion of the event that kicks off the whole conference. Naturally, the biggest thing that Google may have to show off at the event is Android O-related, and the speculation is that they'll be announcing the second developer preview of Android O during the keynote, and then making it available for download that same day so developers as well as interested consumers will be able to load it up on their compatible devices.
Another possibility for what Google may have to show off is Fuchsia. While Google hasn't officially announced anything with Fuchsia yet there have been some rumblings about it since last year and just recently some screenshots were leaked of what the Fuchsia UI design seems to look like. This suggests that they may be close to showing a working prototype of the operating system fairly soon, and with Google I/O coming up next week, there really couldn't be a better time since this would be software-related and Google I/O is mostly for developers. That being said, there is a good chance they may not show it off or even talk about it either, as they were suspected to maybe do something with it last year and it was nowhere to be found.
While not necessarily the most likely, it's possible that Google could have some stuff to announce that revolves around virtual reality and augmented reality, which would mean it would be revolving around the Daydream and Tango platforms. This could be anything from new hardware to just new software, or further advancement of the platforms themselves. When it comes down to it, there are tons of possibilities for what Google could announce at I/O next week from Chrome to Android TV to more Google Assistant-related stuff. Everything is technically up in the air at the moment but it won't be long before all of this public knowledge, seeing as how the Keynote will happen next Wednesday morning at 10 am.