I think they mean in monster statblocks. So, for instance, you don't have to flip through your PHB or other resource and find spell descriptions.
Personally, I'm fine with the Spellcasting and Innate Spellcasting traits as-is, but I don't think it would bother me to see them go. (If it does, I can just add them back in or use older statblocks.)
Apropos of the topic somewhat raised by the reference to The Alexandrian in the original post:
"I don't care for playing games where the mechanics are, or at the very least come across as, divorced from the in-game fiction to too great an extent for my tastes" is a perfectly fine attitude to have. And it's perfectly fine to want WotC to make an effort to smooth over any friction in the interaction between game mechanics and in-game fiction.
The premise that "playing with dissociated mechanics ≠ playing a roleplaying game", on the other hand, is a preposterous absurdity, and the Alexandrian ought to be ashamed to have trotted it out. Not least, when it comes to arguing over D&D, because very nearly all D&D game mechanics - perhaps actually all of them - are both arbitary and divorced from the in-game fiction to some lesser or greater extent.
The substitute for concrete mechanics in any D&D game is DM arbitration. By my reckoning, DM arbitration is also fundamentally "dissociated", no less than an abstraction such as, say, hit points.