I know this a joke theory (mostly), but given how much Star Wars rips from classic scifi works, I think looking at the Foundation books makes a good case for this being viable as more than a joke.
It’s not even viable. In canon, Jar Jar was relegated to being a shunned street performer on Theed where adults hated him but the children would laugh at his clown antics. A Sith lord wouldn’t become that, ever.
I am viewing from intention as written, when written for the films. It seems plausible that "Darth Jar Jar" or something similar could have been an original, but abandoned intention.