Canon is likely saving up for a big showing at Photokina in the fall, would not be surprised if that is one of the lenses announced.
I would also not be surprised if this is not announced, if the outdated 50/1.8 and 50/1.4 have been selling so far they will continue to do so. The 50/1.2 is a unique prestige cash cow not to be easily endangered by a faster 50mm with IS and good bokeh.
If Canon are afraid to endanger their existing products, they will lose out to third party manufacturers. I'm already thinking of a switch to Sigma or more likely Zeiss in the absence of a 50 macro with the build and IS of my 24.
Worse still, Canon risk losing those customers buying into a first DSLR or trading up from crop sensor kit. Nikon have a tempting range of primes, and Sony will have a fast growing selection of quality FE lenses coming this year and next. If those buyers invest in Nikon or Sony kit instead, they will be difficult to pull back.
Canon have proved they are not afraid by introducing the IS primes against L primes. Does the 35L stand head an shoulders above the 35 IS? (I'm suspecting the 35L II must be coming soon)
The 24 IS makes me feel glad I committed to Canon, if a better 50 prime or two is announced then I will be convinced. All 4 of Canon's 50 primes have been neglected for far too long. It's time to bring the 50 and 85 primes up to modern standards. The manual focus on the 50/1.8 ii gives a poor impression of Canon, though the optics are commendable for the money - it's the only lens I have ever felt moved to sell, even after cheap third party OM lenses in my student days.
The kit lenses with wobbly focus rings are slowly being phased out in favour of STM lenses with better build and positive reviews. The more affordable full frame lenses will follow (I hope) with USM and IS, as has already happened at 24, 28 and 35.
If the 50/1.4 has a place, it is as an entry level lens below an IS model with ring USM. That is the path already taken by the 28/1.8 which now exists as a cheap alternative to the 28 IS.
I'm crossing my fingers for new primes this year. Canon already have an outstanding range of telephoto zooms, a strong range of mid range zooms, and an inceasing range of wide zooms.