I think if you structured the surrounding land right, it could be an interesting addition. A Jafar ride would inevitably be a "darker" attraction, just due to the nature of the character.
I think in order for it to work it would either need to be a part of a villain land, as you mentioned, or incorporated into an Aladdin specific area.
If we went around the parks starting with the MK, if you took out storybook circus and replaced it with the "dark side" of Fantasyland (aka a villains mini land) it could work.
I would stray away from including it in Morocco. Although there is an Aladdin meet-and-greet there, that's a whole other debate about not only the origins of the tale, but also the excess inclusion of characters in WS.
For DHS, it could possible fit in an expanded Animation Courtyard, but it would have to flow properly. I'm not sure how to make that work just yet.
AK, there's not really much you can do there I don't think.
I feel you're in pretty good shape if you do a villains land. I think Jafar is a very interesting villain and it would be cool for him to get his own attraction. Looking forward to see what you come up with!