Yes, so to me, the key question is not whether Swift can replace Python's role, but whether it can replace C++'s role, and thereby also making Python's role unnecessary and solving the two-language problem in the process.

I think we can all agree that C++ is a dragon that needs to be slain here. Swift could potentially get close to that for most of the needs, but I still wouldn't bet data scientists would write swift.

As a data scientist, most of my projects have been individual--I'm generally the only person writing and reading my code. No one tells me which language I have to use. Python and R are the most popular, and I use either one depending on which has better packages for the task at hand. I don't use Julia because I don't see enough of a benefit to switching at this point. But I really don't care, they're just tools, and I will use any language, Julia, Swift, whatever, if I see enough of a benefit to learning it. I would just take a day or two and learn enough of it to write my scripts in it.

So I think that's the good news--because of the more independent nature of the work, you generally can win data scientists over to a new language one at a time, you don't necessarily need to win over an entire organization at once.

Getting a company or a large open-source project to switch from C++ to Swift or Rust or whatever, seems much harder.