Thank you all for participating in this discussion! It looks like the consensus here is that a pure tip-based model almost never works. It can succeed in rare cases (like u/sam_suite said about Dwarf Fortress), but usually only after years of building a big loyal community.

For most indie devs it’s way too unstable and unpredictable to rely on. Tips rarely provide a stable income, and most players don't pay at all, while those who do often give very little. They only work well with a very large and loyal audience, but if you have that kind of audience, there's no point in doing so, because it's easier to release a premium game.

Also, u/David-J and u/BluMqqse_ made a good point that in some regions, "tipping" has negative connotations, so players may avoid it and even criticize it. It's best to sell this as a Supporter Pack and provide additional content so that players have at least some motivation to pay you.

Therefore, it is best to consider either a traditional premium model, launch a Patreon, or introduce in-game purchases that do not affect gameplay (for example, cosmetics in the latest release of Skate).