The 17-55 is approaching 13 years and it does not have the wide acceptance of the 100-400L.
The dedicated crop product cycle seems to be shorts all around.
Of course, with Canon... You never know!
They're not going to discontinue service on a current lens....maybe if it gets replaced they will...but age alone isnt a reason to discontinue service...
Op, after reading this whole thread, i think you just need to shoot with what you've got more, the lenses arent holding you back