GNU Guix recently changed[1] the way it handles packaging of rust packages.
The old rust packages got moved to the "guix-rust-past-crates" to help avoid huge breakages for systems depending on the older packaging system. "guix-bioinformatics" used a number of rust packages, defined in the old form, and we needed a quick fix, thus the introduction of the "guix-rust-past-crates" channel as a dependency.
We need to move away from depending on this channel, by updating all the rust crates we use to the new packaging model.