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@Oliver Schick
One of the main reasons for inaction in returning one-way systems to two-way is signal phasing. If you have two-way traffic at a junction, you may need more signal phases, which can be difficult to cram into the usual 90- or 120-second signal cycle. One-way systems help in emphasising certain dominant flows over others, giving them more time at the signals.
If all you have is traffic coming out of a one-way street, and the arm of the junction opposite it is one-way in the same direction (as in the case of the Earl's Court north-south arms) you only need one phase for that, regardless of whether traffic turns left or right, or goes straight on.
With two-way traffic, there will be conflict between right-turners out of one arm with right-turners out of the opposite arm, and there may also be conflict between right-turners and left-turners from opposite arms depending on the shape of the junction.
Resolving this, and then clearing the junction, takes longer, so you may need separate right-turn phases (split phase), or separate phases for each arm of the junction. This is especially the case at very busy junctions. I shouldn't have given you the impression that it's only stacking space that matters, although of course the two are related.