well. you can expect about 7.7, they don't look how you might expect they would at that speed. There are several example videos posted around showing eink video. It's surprisingly good on the 4 and 5's when done right. Even the 3's can do it.
Here's some fun.
And yes. it would be great to make this an extension. it has taken months of work to get here though and TBH it has taken me weeks to begin to integrate this into other things, never mind find a unified audio format and encoding scripts. GM is the man for that, should he ever find the time or inclination but in his absence the demo and code is there.
Interested devs? jump in!