Initially raised in #9305 (comment) (and following comment).

We realized in 2.1 that there is a reasonable argument for plt.plot([1, 1], [1, np.inf]) to draw a semi-infinite vertical line and plt.plot([1, 1], [-np.inf, np.inf]) to draw an infinite vertical line by default (by having the renderer clip infinities instead of masking them). Right now log scale allows both clipping and masking behavior, but linear scale always masks.

Of course this is a breaking change, so I'm just opening this for discussion.