When suggestions of this type come up, especially for causes that don't have existing EA research behind them, my recommended follow-up is to look for people who study this as normal academics (here, "this" would be "ways that grades and grading policy influence student outcomes"). Then, write to professors who do this work and ask if they plan on taking advantage of the opportunity (here, the natural experiment caused by new grading policies).
There's a good chance that the people you write to will have had this idea already (academics who study a subject are frequently on the lookout for opportunities of this kind, and the drastic changes wrought by COVID-19 should be increasing the frequency with which people think about related studies they could run). And if they haven't, you have the chance to inspire them!
Writing to random professors could be intimidating, but in my experience, even when I've written emails like this as a private citizen without a .edu email address, I frequently get some kind of response; people who've made research their life's work are often happy to hear from members of the public who care about the same odd things they do.