Back To The Future’s Christopher Lloyd (who plays Doc) recently talked with Phoenix New Times about the possibility of a fourth movie AND joining the cast of Rick And Morty.
“Well, I think its a matter of, first of all, it’s important if Bob Zemeckis and Bob Gale are excited about doing another episode [of Back to the Future], I think, really, the most important thing is if they can come up with the right idea. I think that’s the challenge is to come up with something that really is as good as the originals.”
He continued, stating:

“I suppose it could happen. I have not heard that they’re looking for that if they’ve made up their minds … hey, here’s something we could do, and they believed in it then they might get going to do it.”

Lloyd was asked if he’d be interested in participating in a fourth film to which he replied he would be “delighted” so long as the storyline was right:

“I’d be delighted,” Lloyd shared. “I’d love to be in a fourth film, if they could come up with the right idea that extends the story and does it as well as the first three.”
Sadly however, Robert Zemeckis, the film’s director, recently shared that “there will not be any more Back To The Future [movies.]”

That doesn’t necessarily mean Lloyd wouldn’t mind being a part of other projects inspired by the Back To The Future franchise.

He continued telling the Phoenix New Times, that he wouldn’t mind lending his voice to Rick And Morty, a show that has taken some serious inspiration from Lloyd’s Doc Brown and Michael J Fox’s Marty Mcfly.
“I don’t follow it closely, but I’ve seen a few episodes and I gotta tell you, I think it’s a lot of fun. I know it’s some kind of parody of Doc and Marty”
As for what character Lloyd would voice, well, he wouldn’t mind taking on the role of Rick’s father, telling the paper that “yeah, yeah. That’d be fun.”
We wouldn’t mind that at all!