If Riot will not make any statistical amendments aimed at regulating champions to Twisted Treeline (ie Crystal Scar Aura), then they at least need to change a few key terrain abuses.
The worst offender here is the wall behind the Nexus, with the runner-up being Dragon's wall. The champions that can make use of abilities to move through terrain have so many undeserved in imbalanced advantages on this map.
Everyone has played games where the enemy Tryndamere pushes the waves while you're respawning, and he will come and dance in your base. He'll fight you, then pop ult and spin through the wall. And it's not even unique to Tryndamere. Flash allows this kind of play too, as do several other champion kits. I am tired of being killed or being denied kills by terrain abuses...in my own base. Your own base should not provide the enemy with combat advantages, but Twisted Treeline does, and it needs to be fixed.
Dragon wall I am less concerned about, but it basically guarantees an escape from a gank for someone sporting flash or some ability in their kit that allows them to move through walls. But it's much less of a concern.
If the Nexus wall isn't fixed, then the Nexus should be granted a tremendous amount of resistances when enemy minions are not present. If they push the waves, and minions are at the nexus, this bonus is lost. A built Tryndamere can destroy the Nexus before anything can be done about it.