One of the frustrations with Android is the lack of updates for existing devices when a new OS update is announced. It looks like HTC and Motorola are working to eliminate that frustration with announcements that their latest products will be updated soon.
The Google Play Edition should see Android 4.4 within 15 days, the unlocked model and Developer Edition within 30 days, and the carrier variants within 90 days.
The fact that the One will indeed be getting the 4.4 update, just after the 4.3 update, means my One will not be going anywhere even if I end up keeping the Nexus 5 I just ordered.
Motorola also revealed that the Moto X, Droid Ultra, Droid Maxx, and Droid Mini will all be getting Android 4.4. There was no time frame reported for these updates.
Many older devices, including the Galaxy Nexus, will not be upgraded to Android 4.4. It is difficult for Google and manufacturers to upgrade these older devices when internals are outdated while it is much easier for Apple to provide updates when they control the entire hardware and software environment.