Simply increasing the AP ratio mid laners get against turrets, or even allowing some of their spells to damage turrets, could be a big step towards allowing classes other than the ADC to push more consistently. I feel that, to some degree, it's pretty hypocritical to justify the current mandatory status of marksmen because they're apparently the only class capable of truly pushing towers, when there is a) an artificial restriction imposed on structures that prevents most AP champions from using their greatest asset against them, despite allowing marksmen to use their own abilities to push harder, and b) an actual ratio in place to allow AP champion to push, which is still being kept so low that marksmen eclipse them at all stages. Some parts of the game do favor autoattacks, but only because they've been forced that way, and I feel there are a great deal many things that shouldn't be autoattack-exclusive (making wards take damage from abilities could help non-marksmen clear them faster, for example, and many monsters could have their MR drastically reduced to let casters kill them more consistently).