I agree 100% that matplotlib is really slow and should be made to run as fast as humanly possible. I would add a (3) to my list above: optimize matplotlib!
OTOH, at least for what I'm doing, the code that runs to generate the data that gets plotted dominates the runtime 99% of the time.
For me, adjusting plots is usually the time waster. Hence point (2) above. I'd love to be able to make the tweaks using a WYSIWYG editor and have my plotting script dynamically updated. The bins, the log scale, the font, the dpi, etc, etc.
I think with your 8 slices examples above: my (2) and (3) would cover your bases. In your view, is the rest of matplotlib really so bad that it needs to be burnt to the ground for progress to be made?
edit: regarding runtime, I'm sure this varies a lot based on usecase, but for my usual usecase I store a mostly-processed dataset, so the additional processing before drawing the data is usually minimal.
Matplotlib is okay, but there's definitely room for improvement, so why not go for that improvement?