Ironically I believe GitHub should play a bigger part in OSS. They and a few other platforms have a unique position which could help to make open source software more sustainable:
Following the idea of "make it as friction-free as possible", something I'd like to be able to do is somehow track my usages of various packages across the course of a month, then divide a set amount of money, say £15, across each of them proportionally. Each project could have whatever amount they "earned" (doesn't seem like the right word, but never mind) automatically donated to them at the end of each month.
A library downloaded 3 times a year might just have users that know how to set up a local cache, while a library used by unskilled teams will be downloaded 15 times every time they run a build.
All your model does is push people to learn how to make local caches, and it also doesn't work at all with FLOSS licenses, since there is a right to redistribute.