I think that merging CLIs and GUIs have a great potential.
GUIs are superior than CLIs on interaction because it gives context of the current state and visual cues. (And no, TUIs aren't CLIs nor are they better than GUIs.) However users still use CLIs - the biggest advantage that CLIs have is that it allows various programs interact with each other, e.g. via piping. That's why we have CLI programs that's sole purposes that are communicating with GUI programs, for example almost every programmer's text editor ships with a binary that can i.e. reading from stdin, opening an temporary file, and spitting out to stdin (or at least gives the capability of doing that) so that we can use it in e.g. moreutils vipe.
It seems Fig is an product that allows the reverse, e.g. tying GUIs to CLIs so that people can use git, curl or other CLI programs in a more interaction-friendly way. I think this is has a great potential, if it's rightly executed (i.e. hopefully doesn't use Electron...?)
PS: The argument that 'every programmer knows how to use CLI, so this isn't needed' is just proving the point - programmers deserve better than an plain-text 1970-era interaction, yet we have to use the Terminal daily to accomplish something.