Bearing in mind the normal lifespan/shelf life of macro lenses and given the fact that it is Canon's newest one and the only one with Hybrid IS, I'd be shocked to see it replaced/upgraded in the next ten years.
Believe it or not, they are somewhat 'due' for a new FF macro lens..........
Nonsense, where has lens technology moved on to since the 100 L Macro came out? Blue goo and coatings, neither of which are enough to warrant the 100 L getting upgraded.
The 180 is well overdue for a remodel and there is plenty of newer stuff to put in it, weather sealing, Hybrid IS, Blue goo, coatings, light weight build (engineering plastic) etc etc.
The 50mm Macro isn't even a true macro lens, it is only a 1:2 life size that needs a dedicated tube with glass to get it from 1:2 to 1:1, Noah used one on the ark to document the smaller animals. This could be upgraded with good specs and remain reasonably priced, that it hasn't speaks volumes for the sales numbers and projections. Who would use a 1:2 "macro" lens over the TS-E45 with a tube? About half a dozen people who photograph flat field reproductions, and Noah's great great great grandkids.
The EF-s 60 Macro, again, what would you put in it that meant it wasn't an L and Canon won't make EF-s L lenses.
The MP-E 65, I doubt if that will ever get upgraded, it has no real competition so why bother? It won the competition in the field of one! IS probably wouldn't be any use in it because it's effectiveness is reduced as magnification increases, it isn't a heavy lens, it doesn't need Blue goo so no upgrade.
I think Canon are happy to sit on their laurels with regards macro, just look at the half arsed unenthusiastic "upgrade" to the Macro Ring Lite MR-14EX II, a new LCD and interface, they gave it the RT interface with no RT!