If you can get one of these jobs, you can get the other, although not necessarily at the same level. You can certainly switch careers between these two, especially early career.

I don’t know about anybody else, but I would see experience in both as a plus on a resume. I think it’s a good idea for SREs in particular to get a dev job on their resume since the person hiring you is going to be a developer a massive amount of the time so it never hurts.