That's not true from what I've seen. High Sierra will be the last version to support 32-bit apps "without compromise". It's successor will still support 32-bit, but apparently with compromises (whatever that may mean), and the OS will "aggressively warn users" that they are using a 32-bit app that will soon be unsupported.
It will mirror the transition that we saw with iOS. Apple has clearly been looking to jettison 32-bit support for awhile now, and with iOS 10 they started warning users. Finally, with iOS 11, they are cutting 32-bit out completely.
High Sierra is like iOS 9 - 32-bit works normally, as expected
macOS 10.14 will be like iOS 10 - 32-bit apps will work, but a transition is clearly underway that is exposed to the user with warnings
macOS 10.15 will be like iOS 11 - 64-bit only with no support for 32-bit apps
This seems to be how it will go from what Apple has revealed so far.