I am using tags to describe the projects (I think that I'm not alone). I would like to be able to sort by tags that would belong to the same project tasks are placed one after the other.
However, the sort of more important priorities. In my case it would be an ideal way: first sort by priority, and already sorted in groups sorted by the tag. Options can be many.

For example like this:
1. Priority 1
    tags 1
    tags 1
    tags 2
    tags 2
    tags 3
2. Priority 2
    tags 2
    tags 2
3. Priority 3