What would be an example of a well-designed, useful feature that doesn’t mesh with the philosophy of the project?

Anything that falls outside the intended scope of the project.

"What if we allowed posting GIFs to hacker news posts and comments?"

“What if we added a GUI based web browser to CURL?”

IMHO a better example is: "Can we make a teeny tiny change to CURL that would allow me to use it as a fetch engine for the GUI web browser I'm making? I can't think of anything else that might use that change, but pretty pretty please?"

This could have been a good example, except curl is not only a CLI, it builds on top of libcurl, one of the most popular libraries for doing HTTP in C. If building a web browser, it’s one of the first candidates for a fetch engine I would reach for.