In order to make more accessible the discovery of article and other page contents (like, wikiprojects), I propose an "always-on column" option for the Table Of Contents. The option would allow to display the TOC embed in a column inside the content space (on the left or the right side). The look and behavior of this column would be a bit like what you can see on the Wikipedia apps for iPad and Android or Wikiwand, except for the numbering. The column may be hiddable/colapsable.
The skin (Vector, Monobook, Timeless...) outside the main content space wouldn't have be affected by this option but still could integrate it more tightly if developers want to.
Here are some screenshots I took from the Wikipedia app on iPad (you can find them with titles and descriptions in this category on Commons) and the same articles on Wikiwand: