I was wondering whether there was interest in working on an "axis-swapping" API, which would allow an Axes to use its x axis as a y axis and vice-versa (or at least figuring out whether this would be possible). The idea would be to replace all the plotting functions that possess variants where the two axes are swapped (hist(..., orientation="horizontal"), fill_between/fill_betweenx, etc.) as well as those for which such a variant is being proposed (#5856).

See also https://mail.python.org/pipermail/matplotlib-devel/2016-June/000472.html (and the earlier messages in the thread), which discuss the usefulness of sharing various pairs of axes among the three axes of a 3D plot with the two axes of a 2D plot (for an interactive orthogonal projection plot). I don't know how well 3D axes support sharing but perhaps this would again be much easier to support with "axes relabeling".