You can already get Jelly Bean for the Galaxy Nexus, if you're willing to do a manual install. I've been running Jelly Belly[0], an LTE Jelly Bean rom, on my LTE Nexus for the last couple of days. There were a few issues with Jelly Belly v2.1 (tethering and camera), but as of Jelly Belly v2.4, it's been running without any hitches, Google Now and all.
Google announced at I/O that JB would be coming to nexus devices in July and the Galaxy Nexus on the Play Store is supposed to ship with JB in 1-2 weeks. So pretty much.
0: http://rootzwiki.com/topic/28677-rom-jelly-belly-v26-0709201...