I know the main reason why the Mac Pro has options for LRDIMMs for terabytes of RAM is specifically for audio production, where people are basically using their system memory as cache for their entire instrument library.

I have to wonder how Apple plans to replace the Mac Pro - the whole benefit of M1 is that gluing the memory to the chip (in a user-hostile way) provides significant performance benefits; but I don't see Apple actually engineering a 1TB+ RAM SKU or an Apple Silicon machine with socketed DRAM channels anytime soon.