I got a message from support saying that this feature will be in Version 7.9.9, which is coming soon. Here is what they said about it:
"There is a filter in the automations that does kind of what you described, but it is focused on one specific email at a time:
We prepared a new option for the v7.9.9 under the "Statistics" filter for users that have never opened any email. Maybe something like this would do the trick ?
It selects the AcyMailing users that never opened any campaign, and that have been existing for at least a year."