I think the 40k minimum is just so that some of the smaller artists aren't just earning a few dollars (which they can't redeem) and helps sort/filter through comics so that they don't just have lots of small comics that can't withdraw the cash.
I do know some artists that get millions of view per month so there are a small amount of creators that draw in enough viewers that this could work for them at a substantial level, however for me, it'll just be good as some extra cash especially with the help of the credit system to give artists a little extra. But yeah, unfortunately ad revenue only really works well if you have a larger following/viewer count, regardless of whether it's youtube, webcomics, video games etc.