Canon rumours have just posted an article stating the possibility of a Sigma releasing a 24mm 1.4 in the near future.
From canon rumors:
“We’re told that Sigma almost has a 24mm f/1.4 DG HSM Art lens ready. An announcement could come this year or early next year. The build quality and performance will rival that of the Sigma 35mm f/1.4 DG HSM we’re told. The lens will be a little more expensive, but Sigma hopes to keep it under $1000 USD.”