It largely depends on how you are designing your hack in the first place. Obviously, a typical hack that follows conventions similar to other 2D Mario platformers should be designed with similar level length, as too short could be rather unsatisfying while too long could really push the player's patience, especially if you are expecting the player to avoid making mistakes.
If you are making a hack that doesn't follow SMW conventions, you can probably get away with larger levels. For example, a hack with a health system that affords more mistakes for the player can in turn make longer levels more tolerable, as will the use of the Multi-Midway Points patch--though one would need to make sure these levels have enough substance to their themes to maintain the player's interest. Similarly, a hack that is designed more around exploration could also stand to use larger levels.