[SUGGESTION]
Since in sigma, new maps may be available, how about a random map system for end game? Kinda like having new dcow maps but with new monster, bosses and environment. And having a system where you can upgrade these maps with modifications, just like how you can modify items using shrines. A good draft for this by having monsters in lvl 100 areas drops a "map item".
Map items may even vary, like having 10-20 types of maps, based on the areas in the game, like for example, a "Cathedral Map" will produce a map with similar monster, layout and even a special boss to that particular map as the Cathedral area in Act 1 or even a "Summit Map" that will create a map entirely based on the area in Act 5. Also to mention these map items are consumable and will be gone after use, just like how the Tome and Wirt's Leg is used up when opening a cows map.
Now we can modify this "map item" with having better drops, ea. a Hidden shrine cubed with the map item will modify the map to have a chance of having an extra boss, or a fascinating shrine cubed with the map will produce a map with a bias of dropping gems and runes, or a Stone shrine cubed with the map will modify the map to have a physical damage immunity in exchange of a bonus magic and gold drop in the area... the possibilities are almost endless in this kind of system.
In Torchlight II, this system is implemented with the limitation of modifying the map, and in Path of Exile where you can modify the map to the point of having so much modification(means more MF and drop quantity as well) it's almost a gem to make the best map out there. And also to mention Unique maps where it randomly drop in areas where maps can drop. These unique areas have unique challenges too just like how uberlevels work in this mod.