People have the wrong idea about this. I have no particular affinity for lisp and I doubt the rest of the team does either. It’s just that nobody to date proposed a reasonable alternative, let alone offered to help with the proposed massive project.
Anyone that suggests toml, json, and the like, is aware of only a fraction of dune’s feature set, nor is aware of the kind of contortions it would take to fit dune’s features into these simple formats. Anyone that suggests OCaml doesn’t have answers to the most immediate questions such as “how to produce proper error messages?”, or “how will it work in watch mode?”.
The door is wide open to do better than s-expressions. The team today just doesn’t have the bandwidth to design, implement, and transition the entire ecosystem to a new format.