Nexus 5 debut is anticipated by various websites since there are reports about Nexus 4 being out of stock with several sellers. This also includes Carphone Warehouse who was one of the first sellers to have offered the device.

Another site Phones Review suggests that the Nexus 4 stock shortage could be temporary as there are fresh campaigns.

The white Nexus 4 also vanished from the Google Play Store a few days back, which stroked the speculation that the Nexus 5 announcement could be sooner than expected.

Nexus 4 release date last year was in October / November which makes some people speculate that Nexus 5 release date will be same time this year. That will also help get the Christmas shopping spree.

It is also possible that Google may time the release of Nexus 5 with some of its worthy (in some cases better) competitors in the second half of 2013. Some of the phones expected to be released then are iPhone 5S from Apple and the third-gen phablet Galaxy Note 3 from Samsung.

Google Nexus 5 rumored specs:

Nexus 5 leaked / rumored specs seem to suggest that it will have a 5.2-inch OLED screen with a 1920 x 1080 (1080p) resolution. However some industry watchers are suggesting that will only have a 4.5-inch 720p IPS screen.

A 2.3GHz quad-core Snapdragon 800 processor is expected to provide the thinking power. It will have a place to play in a 3GB RAM and either 8 GB or 16 GB of internal storage. There was some talk from google on improving the cameras on Nexus line. So it is possible that the next camera model will be made by an established camera manufacturer like Nokia. It is expected to have a 16MP sensor. Another leaked feature is the 3140 mAh battery.

It is suspected that that it will have the Powerful Key Lime Pie platform.

Nexus 5 debut price is rumored to be around $US199. Some think it may be around US$ 299.
Sidhtech suggests that LG Nexus 5 could be based on LG Optimus G Pro. Their logic is like this:
LG Optimus G Pro is a follow up to the LG Optimus G, on which which the LG Nexus 4 was based. If LG are going to make another Nexus device then it would be based on the successor. This is similar to Samsung Galaxy S & S2 being the basis for the Nexus S & Galaxy Nexus.

The LG Optimus G Pro is said to have a display of 5 inches / 1080p, Snapdragon S4 Pro 1.7GHz quad core processor, 32GB of storage, 2GB of RAM, 3000mAh battery and a 13 megapixel camera.
This fuels the speculations that Nexus 5 will debut with similar or slightly better specifications.