> A repl/notebook thing that is running on a .venv preinstalled with stuff defined in some config file.

So, create a project as a playground, put what you want it to include (including something like Jupyter if you want notebooks) in the pyproject.toml and... use it for that?

What do you want a tool to do for that style of exploration that uv doesn't already do? If you want to extract stuff from that into a new, regular project, that maybe could use some tooling, sure, that would take some new tooling.

Do you need a prepackaged set of things to define the right “bunch of stuff” for the starting point? Because that will vary a lot by what your area of exploration is.