The one that is currently up is pretty outdated; I was just curious if one such as myself could update, package then upload it?
assaultcube is currently synced directly from Debian. You might consider reporting a wishlist bug against the package in Debian.
If you are interested in trying to do it yourself, this might be a good place to start:
You would also need to update the associated “assaultcube-data” package. Then you would need to follow the sponsorship process to get the package uploaded.
There is already an open bug about this in Ubuntu.