Seems an end user nix interface way better than having to fiddle with shell.nix
However it lacks documentation for more specific needs, like how to override a package or pin a version? I didn’t find any documentation for devbox 
I feel the urge to cite the incumbent in this occasion: GitHub - numtide/devshell: Per project developer environments
Although it’s hart to beat the marketing muscle of 1.6k stars in 23 days (?).
Is it possible to use poetry2nix or mach-nix with devshell to create a environment with python modules?
There is no ootb integration, but it is definitely possible. One could also write an integration module that takes care of the interface.
In general, though, devshell works with packages = []; (just as the traditional devshell) or with commands = [{}]; for something more exciting, that will be displayed in entry as MOTD or via the built-in menu command.
There are other options to set env variables or write special purpose init scripts.