I would love to have some sort of macros in Discover to make creating segments more scalable. For example, if I wanted to create a segment for each visit number (first, then second, then third, etc) it can be pretty tedious. Similarly tedious if I wanted to create unique segments for each of my top X marketing channels. It would be cool if I could enter a macro in the criteria of a single segment and then Discover would read that and know to make multiple segments based on the variation that the macro indicates. it is almost like taking the scalability of breakdowns but adding the flexibility of other segmentation features (different container scopes, include/exclude, etc)
With this in place you could then easily make cohort reports. For example, I would create a segment for visitors that had a visit where visit number equals one and the month of that first visit was equal to a macro that listed the last 12 months. When I applied this to the report it would then automatically create 12 segments--one for each month in my "month macro".
If you were to do this I think that it would be important to not just auto-generate a bunch of separate segments but to keep it as a segment group that you can go back and edit all at the same time (instead of having to go back and edit a bunch of mass produced segments.)