If something hasn't happened yet it indicates that if it does happen it will happen later. For example, since pigs haven't flown yet, if they do fly, it will have to be later.

Seriously, though, I think the researchers were trying to put a positive spin on a negative result but went too far.

I suspect they meant the former finding, i.e.: "volume increases in more brain areas, including the cingulate cortex, insula, corpus callosum and sensorimotor cortex"

That still doesn't make sense. They take it is a forgone conclusion that volume increases will _eventually_ result in cognitive benefits, but provide no evidence or sources to support that notion. Of course, it seems to intuitively make sense that "bigger brain means smarter", but in a science article I would imagine they would be more rigorous about substantiating things.