[eponeponepon]

I think they're solutions looking for a problem.

Tips in the service industry are functionally a means of bolstering income for people who are, by and large, distinctly low-paid workers; developers, even on the low end of the scale, tend not be. I think it's also fair to say that most (most - I realise it's not all) active contributors to open-source projects have day-jobs that provide adequate-or-better income. So what would motivate a common-or-garden developer to court for tips in the first place? And how would a "tip-sized" tip even be noticeable to someone on a developer's salary?

[edit to add: perhaps the issue is the metaphor? A "tip" is roughly what I described above - but it's not actually any different from a "gift", a "donation", or myriad other terms (except, yes, in legal terms of course).]