It would be interesting if there were a way to allow X fortifies with return to attack and Y fortifies with no return to attack. Currently, you cannot have both.
could be interesting.
+1 Nice feature. Don't know how 'important' it is; i.e. would it make any board design "better," or enable a creative play-mechanic, but could be interesting for sure.
Not sure if it could be considered 'important' compared to some of the other designer requests, but I would use it if it existed.
Or alternatively - if you could only switch between phases N number of times. Either for back to place or back to attack.