Taric and Yorick both have Sion-level updates (in all aspects) in development- Taric's should be out either by the end of the year or very early next year and if everything goes as planned with Yorick, I suppose that his update will be out somewhen around late 2016.
Other than that, a lot of champs were considered to be given a VU (or more). IronStylus confirmed on his stream that, right now, all VUs in development are accompanied with Gameplay updates (the reason for that is that they- Rioters- think that they will not have a chance to touch champs like Fiora and her visuals any time soon/ever if they wouldn't have worked on them now, with her Gameplay update).
I asked IronStylus a couple of questions during his stream about a few champs ("What do you think of X's visuals") and I asked about Jax, so I summed up his answer: Jax is clunky (Animations-wise)- He's a funny and cool character in general. He needs to be figured out ("What is he?") thematically and there are some nice things that could be done with him.
I did not ask him about Panth unfortunately. I do remember though that he wants to work on him and tie him more into Mount Targon's visuals (when they figure out what exactly they are- The cohesiveness of Mount Targon's art style), as with Leona (which he wants to update as well when the time is right).
I suppose that they are not being worked on (Visually), unless they have a gameplay update in progress.