Technically true, we can't predict when or if specific mutations will or won't occur. We do know this virus has in fact already mutated significantly on two of these axes though (virulence and vaccine resistance), as variants have emerged that vary in some degree in those ways, and it seems somewhat optimistic to think it won't continue to do so.

Fortunately it's not mutated too much in terms of vaccine resistance. Delta seems significantly more resistant to single doses than Alpha but a second dose so far does the job. We've only recently exposed the virus to large numbers of vaccinated people though, so there's not been much time for resistant variants to gain an advantage.