https://gitlab.gnome.org/GNOME/librsvg https://people.gnome.org/~federico/news-2016-10.html
(I do not necessarily endorse this, as I find the dependency on a Rust compiler of very recent vintage, to be much more annoying than depending on any decent C compiler from the last 7 years or so.)
Perhaps you can list some and why they were casualties of the Rust language rather than reasonable cleanup that would have happened in any rewrite?
a) It being acceptable to upstream is mandatory to receive a bounty, so a starting point might be: pick projects whose maintainers are sick of dealing with ASAN reports! b) A huge number of people get their libpng or anything else via a package manager like Debian. Debian packages libpng from upstream. If libpng changes something about it's implementation, that'll be reflected in a future debian release.
This is going to be a long process, but we firmly believe the question has to be "how" not "if". If you've got better ideas for how we can promote the transition to memory safe languages, please let us know!
The number of times I've seen something that amounts to a 1-3 line code change being discussed for hours is absurd. If you are a new contributor who wants to help out by writing code it often feels like you are making the maintainers work harder than if you had done nothing for the project.