Coming soon to a Nexus 4 near you!
Sascha Prüter states in a post to Google+ that the build is “locked and loaded,” indicating in the comments that LRX21T is destined for the Nexus 4 some time soon:
Just Nexus 4 for now. Our goal was to use as many letters as possible for all the different devices ;)
Soon, not sure when exactly but shouldn’t be too long. Staging the factory images always takes some time.