This is not correct. There are at least three big bioinformatics clusters where Guix is used quite successfully (I know of large-scale deployments in Germany,

This is not correct. There are at least three big bioinformatics clusters where Guix is used quite successfully (I know of large-scale deployments in Germany, the Netherlands, Australia). One of the deployments with 250 cluster nodes and uncounted GNU+Linux workstations is managed by me. I'd say it is very much usable and in fact used in production.