I agree, Henrik.
However, IF this movie ever gets made, they are going to try to get bona fide "stars". As great as DeCarlo and Smith were, they had mostly starred in B-Movies, and while they were recognizable, they were not as famous as, say, Elizabeth Taylor.
With the dearth of film musicals today compared to the 50s, producers are going to want a big, box-office draw. This show is exceedingly hard to cast we with the acting and vocal demands, and, in the past, the "stars" have not given me faith for a film of Follies (Sweeney, Les Miserables). And trust me, "smaller" names such as Brooke Shields or Toni Collette are never going to cross their mind, as perfect as they may be.
They would rather have a lack-luster, washed down hit, than a risky film of substance.
"Sticks and stones, sister. Here, have a Valium." - Patti LuPone, a Memoir