Wherefore art thou, KTU84F? Huh. Doesn't have the same ring.
Apparently something has gone wrong over at Sprint, because not only have we not seen the 4.4.3 KTU84F software update headed for any Nexus 5 units, the Sprint support page has removed the brief mention of 4.4.3 from its update chart. Previously it was scheduled to head out between Monday, April 14th and the following Monday. The update is a big deal for Sprint customers since it opens up two new Spark LTE bands, but the other changes to Android seem to be minimal.
Whether Sprint jumped the gun with the original update announcement, or some kind of technical problem forced Google to stop the process maturely, we really can't say. But the full update can't be too far away if Sprint was confident enough to post the support for it in the first place.
Update: The forum page, now locked, has been updated to say:
Important Note: Due to an issue with the software, this update has been pulled out. Will update this space as soon as a new update is ready to roll out.
We have not been given details on why it was removed. Once we get more information, we will certainly let you know! We don't intend on ignoring this situation, we just need to make sure that everything is corrected before launching. We want you to have the update too! We hope to get this taken care of soon so that we can get all of you guys some answers! We understand that waiting can be difficult and we appreciate you being patient while the bugs are worked out.