I like it the way it is for now. The current case carries the sixteen rare and semi-rare cubimals.
The seven that don't fit are common.
Anyhow, as it stands now sixteen seems to be the max size for bags and there are probably good reasons why the developers have chosen that number. Perhaps we should wish not for a larger case but for more new cubimals. Nine more would bring us to a total of thirty-two and fit perfectly into two cases.
New cubimals please :)
But if they increased the box size, then the collection still wouldn't fit after it is inevitably expanded.
(also, this has totally been asked before. I wish the new post page would include a search field and a prompt to search to see if your question has already been asked!!)