The plt.subplots function in very practical for creating a large number of axes simultaneously, but (afaict) always puts them on a new figure, which is impractical e.g. when embedding matplotlib in a GUI, where a Figure object may be created early on and then populated with some axes later.
I would thus suggest providing the same functionality to already existing Figure objects, e.g. by moving the implementation of plt.subplots to a Figure.add_subplots (or Figure.set_subplots, as it may make sense to clear the figure before) method, and have the plt.subplots function be a thin wrapper that creates the Figure and then calls its add_subplots method.