161-1 V3 carts can be modified and reprogrammed, which basically results in the removal of all the junk bootleg titles, and the addition of most of the missing games in the Neo Geo library (there are still a couple games that won't play correctly). A lot of the bugs that plague the 161-1 (crashing, bad sound etc) are also fixed after modification.
Because of that, V3 carts became incredibly desirable, and all stock was pretty much cleaned out. Maybe more will be made in the future, but since multi carts tend to already be built from scavenged parts, I don't think anyone knows for sure if they will be back.
You can find more info in the megathread on 161-1 development, as well as a build thread that
@rewrite wrote some time ago.