I certainly don't want to see that in a one commit. A PR has one more more commits, though.

The commits in a PR are already a stack of patches, and so PRs are already "stacked" as they are.

If feature X depends on the refactoring (cannot be rebased on the un-refactored upstream), it's part of the change; you can't just merge the feature and not the refactoring.

If the two are separable that way then, sure, it makes sense to ask for them to be separate PRs.