He's probably not going to get rich off patreon donations. The only developers that are doing well on patreon are being sponsored by real companies (or making adult games).

For example vue.js has 100k github stars and the creator is still only getting 15k a month on patreon and a good chunk of that comes from only a small handful of $2000 tier company sponsors: https://graphtreon.com/creator/evanyou. So that's probably a rough upperbound on how much the donation model can support.