When users attempt to launch a 32-bit app in 10.13.4, it will still launch, but it will do so with a warning message notifying the user that the app will eventually not be compatible with the operating system unless it is updated. This follows the same approach that Apple took with iOS, which completed its sunset of 32-bit app support with iOS 11 last fall.
This is good. I would prefer other companies, too, take a more aggressive approach towards deprecating outdated technology in consumer technology.
I’m certain this is one step toward moving away from Intel chips. A chip that has no 32-bit hardware at all is going to require a significantly less number of transistors and therefore less heat / more room to do something else. It’s also much easier to emulate or transpile the Intel code if you’re only dealing with one (much cleaner and newer) arch.