Cate Blanchett has already been tapped to play legendary actress Lucille Ball. Though the original I Love Lucy was filmed in black and white, Ball was perhaps just as well known for her vivid red hair (the iconic look forced her to wear a wig for her final Oscars appearance). Blanchett isn't exactly a dead ringer for Ball, but she's a superb actress and it'll be fun to see her play a comedian.
Cate Blanchett won an Oscar for Best Supporting Actress for her performance as Hepburn in The Aviator. It's a tough act to follow, and even tougher when performing alongside the actress herself. Ball appeared in a film alongside Hepburn around the time that she met Arnaz, so it's likely she'll make at least a cameo appearance. Carey Mulligan should take on the challenge - she resembles Hepburn enough to plausibly play the actress. We loved her in Drive and more recently in Inside Llewyn Davis, and we think she's up to the task.
Vance's character Ethel was married to Fred Mertz, played by William Frawley. Frawley was 10 years Vance's senior, but they made a dynamic duo who kept up with Lucy and Desi's antics. Bill Murray would make a sublime Frawley.
The Cuban-born performer, vaudevillian, and comedian is less Hulk than homemaker, but we still think Mark Ruffalo would make a great Desi Arnaz. They have a strong resemblance, and Ruffalo has a definite funny streak.
Ball and Arnaz both appeared on Bob Hope's show during their reign as the monarchs of comedy. Ball even starred alongside him in 1960's The Facts of Life, and they presented together in her final red carpet at the 1989 Oscars. We'd love to see Hope make a guest appearance, and who better to play him than fellow Brit and funny man Martin Freeman?
Ruffalo's co-star in The Kids Are All Right, Annette Bening would make an excellent Ethel Mertz. Though not much older than Ball, Vivian Vance, who played Ethel on I Love Lucy, was her frumpier foil.