In iOS has already happened, since iOS 11 no 32-bit app works on devices with this version installed. However, Apple takes much longer without accepting this type of apps in the App Store, as long as the change is gradual.
Something similar is happening in macOS, as from January 1, 2018, no 32-bit app can be published in the Mac App Store.
In a new post on the developer portal, Apple has alerted the community again about this change. In this way, they want the developers to update their apps little by little to work on 64 bits:
As a reminder, new applications sent to the Mac App Store must be 64-bit compatible as of January 2018, and Mac application updates and existing applications must be compatible with 64-bit applications as of June 2018. If you distribute your applications outside of the Mac App Store, we strongly recommend that you distribute 64-bit binaries to ensure that your users can continue to run your applications in future versions of macOS. The latest version of macOS compatible with 32-bit applications without compromise is macOS High Sierra.
So, not only will stop accepting 32-bit applications from 2018 but by summer next year will directly stop working on Mac computers with the next version of macOS.
macOS High Sierra is the latest version to work with the architecture of 32 bits
For us, as users, there will be two important changes. The first one has to do with speed and performance, 64-bit apps work incredibly better than apps in 32-bit architecture.
However, it can also be that many apps that we currently use and are abandoned by their developers stop working. If you have one of those “classic” apps that you find incredibly useful and do not want an alternative … surely you will need it.