Technical knowledge, vision, purpose, drive, experience, and training are FAR more important than gear in achieving what you want. You can get far more bang for the buck by working on those things than by waiting for the Next Big Thing. It's fun to drool over new gear and rumors of new gear, but drool isn't a tool. That said...

Photokina and CES and NAB are the three main convention and trade shows where manufacturers introduce new gear.

Photokina 2018 will be held on the last five days of September in Cologne, Germany, 2018. Photokina has no 2017 date, but after 2018, they plan to convene annually, instead of every other year. Photokina is traditionally the largest trade show in the world, where the biggest announcements are made.

The Consumer Electronics Show (CES) 2018 will be held in Las Vegas, NV, from January 9–12, 2018. It is a general electronics industry show, and the second most likely place for manufacturers to announce or display new gear.

NAB, the National Association of Broadcasters show and convention, is to be held April 22–27, 2018, also in Las Vegas. It is primarily dedicated to broadcast audio and video, and filmmaking. So hybrid camera manufacturers tend to be there with new goodies.

Review sites typically have preview articles on announced gear, and sometimes get seeded with new cameras before they are officially released, so they can start reviewing them. http://www.dpreview is a good example.

There are various vloggers on YouTube and bloggers on the Internet who love to speculate about new gear from camera manufacturers. Many of them are pushing for features they want or dream of, rather than providing any factual information. SMART manufacturers do everything they can to keep their developments secret until they know they can deliver them. Still, you can Google "new camera rumors" and find more reading than you can consume in a lifetime.

Modern cameras can potentially last longer in the market, since they have updatable firmware. A manufacturer can introduce new features, tweak existing ones, refine capabilities... So cameras can become more than they are at launch. The four principal mirrorless camera makers (Fujifilm, Olympus, Panasonic, and Sony) have been very good about using firmware updates to add and refine features, rather than just fix bugs.

You can chase the latest and greatest, but if you need a camera today, you need it. Cameras have a market life of 12 to 48 months. The more capable they are, the longer they stay in the market. Lenses, on the other hand, are updated at much longer intervals (five to ten years, in many cases). My take is that you can always trade gear when you need to. So buy what you need and will actually use.