Instead of required dimensions, having the option to specify a required aspect ratio, e.g. 4:3 or 16:9, would be really handy. Maybe there would also need to be an input for the tolerance, so that 401×301 could still pass if 4:3 was required.
This has been requested in the past, the best way to bring this to the developers attention would be to contact them directly.
I created custom filters for this a long time ago, but I do not know if they still work.