[Nexus 5 Q&A, Help & Troubleshooting] lightskies:
The more I think about this, the more I become certain that the N5 will be released at the Play Store press event on October 24. Here's my logic:

1. The invitation

Everyone is expecting a Nexus 5 announcement any day now. The Play Store will obviously be selling the N5 when it comes out. The event invitation Google sent out says "Join us for a night out with Google Play... Music, movies, games..." Those things would be a natural fit to show off a new phone and OS release. Normally Google would tease the new hardware if for no other reason than to make sure that the correct press/tech people showed up for the event, but they don't need to this time around (more on that below).

2. The iPhone Tsunami issue

There have been reports that "it has been confirmed that there will be no new hardware at this event". AFAICT, these are just rumors and there has been no such confirmation by Google. This is important because they would want to manage any potential expectations accordingly if there really was going to be no hardware.

Remember a couple of years ago there was a tsunami in Japan that closed some electronics plants and delayed a new iPhone release? Apple had a press event scheduled and everyone was expecting a new iPhone (because every new iPhone had been announced at an event at that time of year). But Apple took the extraordinary (for Apple) measure of pre-announcing that there would be no new phone announced at the event. They did that because they didn't want an auditorium full of highly disappointed attendees at the event. They prepped the attendees on what to expect to avoid a giant disappointment.

I think Google would be doing some more active expectation management if there were definitely going to be no hardware discussed at the Play Store event.

3. The embargo issue

I think it's safe to say that the various tech/news sites already have N5 samples and are under embargo right now. That's how the tech/news universe works and there's no reason to think it would be any different for this product. There is some hint that the embargo might end on October 25, which would line up perfectly with the Play Store event. The day after the event, the embargo ends and the floodgates can open. Makes lots of sense.

This is why Google didn't need to tease new hardware on the Play Store event invitation. All of the tech/news sites that should show up for the big announcement already know that their embargoes end on the 25th. So when they saw the invitation go out for October 24th, they already knew that hardware would be included.

4. Kit Kat clue

On October 16, the Kit Kat twitter account sent a tweet that read, "Sometimes you have to look for the clues" with a picture of the text "THIS IS IT". Looking backwards, that would have been around the date that the Play Store invitations were mailed out. Stories started showing up about the invitations on the 17th or 18th. Connecting those 2 items together gives a pretty good indication that the big reveal will be at the Play Store event.

At the time everyone was guessing that the "S" in that picture was supposed to be a "5" meaning there was 5 days remaining. What if it was simpler and they were just letting us know that this really was the big announcement?

Just some thoughts, of course I could be wrong...