1. This would break saves, but could be implemented with another element/wall. (see other threads)
2. Use TTAN with gaps in it. (It still blocks pressure within a radius)
3. A Legitimate question. The best answer I can come up with is it's too hard to code. Even TTAN was built with a radius.
4. Put portals on either side of WALL. Profit
3. walls are 4X4 because every force grid is: pressure, velocity, (not sure about) newtonian gravity. Thats why strong bombs cause pixelated pressure displays. If TPT were to calculate pressure for single pixels, it would take 4X4 times as long (if the algorithm was left unchanged).