For me, a huge boost in my gameplay experience will come from the market experience. Since I always bulk rent every two days (most of the time similar cards), it will be nice to be able to do it in just few clicks.
My idea for this is being able to make a groupings/template for my usual card rentals, including specific levels and foil type for each card.
The feature that I am using as an alternative for this is the favorites filter in PeakMonsters. However, when I am bulk renting, it is still time consuming to manually check/input the levels that I want for each card.