We started building the wip-ungrafting branch a week ago: https://ci.guix.gnu.org/jobset/ungrafting
Some progress has been made, but not enough. This is partially due to <https://bugs.gnu.org/48574>, and also due to inefficient building of expensive bootstrap paths (namely, every Rust package derivation tried to build the entire Rust dependency graph concurrently). I just rebased the branch and pushed again.
