Very difficult to speculate here, when you cross the terabyte barrier on a single file as will happen when VR edition comes to mainstream, you imperatively need a copy on write file system with block hashing along with full ECC memory as master original VR products demand (as yet VR is more sensitive to bit riot phenomena than other media).I don't think they are. They looked into it, decided that HFS+ was good enough. They decided that their devices did not need that much storage and one should buy storage from all the great storage solutions on the market. They focus on what parts of the market they want.
In general Btrfs or similar file sistem is an must for any future workstation that should deserve any respect. Is not something that am guru simple can said not mainstream do not need copy on write neither hash protection against bit riot, this is actually a need long foreseen (why you think Apple spent millions sponsoring ZFS, the problem is that ZFS become a monster with insane ram requirements impossible to afford by mainstream pc, also some pro workstations do not implemented it, on the other hand here is BTRFS w/p GPL intoxication and now ready for consumers, and while a copy on write file system allways require more resources than other FS is on the reach.
It's very difficult to speculate why Apple removed raid tool GUI and much more to speculate about the new raid or FS.