Ok, that's a pun, isn't it.
Theo, you probably want to help project viability (and your investment on it). That's fair and reasonable.
What I don't understand is why you ask to exclude, from receiving new releases (enhancements, bug-fixes etc),
those users who can't or don't like to make donations?
Such a discrimination, before anything else (and besides being anti-social behavior, as well as,
a license infringement), is not smart . In fact, at the end of the day, it will damage the project.
Think you "why"?
PS1: I repeat, donations are (and must always be) highly encouraged, since they can greatly help
open source projects. That's one (and good) thing. Restricting distribution to donators only, is an other (and bad) thing.
PS2: Any GPL-ed open source software, as you may know, is based on some fundamental principles;
one of them is free distribution to the public. "Free distribution" is part of an agreement,
it's not an act of charity made once a year or so. Anyway, that's my opinion, I hope it may (or may not) be useful.