We've got word from Bandai America, the next issue of 4" Alien Collection figures are a bit late. But the good news is the next series will arrive by June. This series will include both Alien X, and Highbreed action figures. Other expected characters in the assortment will be Goop, Brainstorm, Big Chill, Spidermonkey, Echo Echo, Ben, Jetray, Humongousaur, Chromastone, and Swampfire.
A word of warning on availability. These assortments are expected to hold only one each
of each figure, including Highbreed and Alien X. So those figures are going to be hard to find.
Also, with this series we will see the last of Ben Tennyson for a while. Alan as Heatblast, Kevin 11, and DNA Alien are not expected to re-appear, at least not anytime soon. This may also be the only series that includes Highbreed.
The next 4" Alien Collection release, later this summer, will introduce the new Upchuck. Gorvan will return so you have a chance to get him if you missed that figure earlier. Also, Alien X and Goop will return with the next series, so you have another chance to snag them--if Bandai stays on track with announced series.
I'll most more info later on the other Ben 10 series releases for this summer.
Update 13 May 2009:
Highbreed will include an attachable chest plate. Look for this series to show up mid-June to early July. Its too bad about the long wait.