Flagged, as a click-bait headline. I'd rephrase to "macOS 10.13.2 update enforces 2048-bit SSH keys; smaller keys forcibly unsupported." (or something along those lines).
RSA key sizes < 2048 have not been recommended for a long while.
...and that's a good thing. Short: they deprecated insecure key lengths (<2048)
You can still use alternative SSH clients if you really need to use them