Reading the upstream changelog it seems that a load of "breaking changes" came in 0.10 with those since then being relatively minor. I've taken a priliminary look through the rdeps and most of the important ones seem to have updated to at least 0.10 upstream.
So my gut feeling is to start preparing an update to the latest version (0.12) and see how things go. Does anyone else have any opinions? elan only uses pulldown-cmark at all because of a debian patch. mdbook uses 0.10 and has a comment not to upgrade because it's "part of the public API" but I don't think that is massively relavent to Debian. rust-cursive-core upstream release uses 0.11, debian is currently downpatching upstream git uses 0.12 and upstream made no code changes when switching to 0.12. rust-ruma-common upstream seems to have moved use of pulldown-cmark from the ruma-common crate to the ruma-events crate and updated to the latest version, code changes seem minimal. rust-skeptic still uses 0.9 upstream. Seems kinda dead upstream. no rdeps. rust-upstream-ontologist upstream has an optimistic dependency allowing any version newer than 0.9 rust-version-sync latest upstream release uses 0.9, upstream git uses 0.11, fairly minor changes upstream when switching from 0.9 to 0.11 rustup version in debian uses 0.9, upstream git uses 0.12. Upstream changes seem moderate.
