A new 50mm 1,4 (with a real USM) would be quite nice...
The 50mm f/1.4 is one the older lenses in Canon's lineup and, yes, the micro USM really needs to go (had mine repaired last summer). I'm also hoping, as with most of the updated lenses released in the past few years, that it gets a shorter MFD. The 28mm f/1.8 and 85mm f/1.8 are of similar ages (all three are in the 1992-1995 range), but at least they have ring USM and better build quality.
The 35mm f/1.4L is the most likely candidate, as all of the other sub-telephoto "L" primes have already been replaced/updated. The long-rumored update to the 24-70mm f/2.8L is another possibility.
As for the non-USM EF lenses (35mm f/2, 24mm f/2.8, etc.), I don't see them getting updated anytime soon. They certainly don't qualify as â€œhigher end short focal lengths," as the posted rumor states.