CI/CD

Pijul as git or hg or any other is a VCS, so what are you talking about? If you mean web-service like GitHub with social things and CI/CD services, so yes, nest have CI/CD with nix. But mostly you shouldn’t host your huge project on the Nest because, as I’m absolutely sure, you as anyone other should create your own host (public or private) to support decentralization to prevent github-like centralization situation. Pijul was created with decentralization in first place in mind.

Not tested with big projects in production

Not publicly. Many private projects, personal and in-company, that uses pijul are existing. Personally I have one HUGE personal. Also I worked for two companies where pijul is used.