Worth noting that iOS HFS+ already had some non-standard features [hacks] that Mac did not use like encrypting files with different keys based on the data prote

Worth noting that iOS HFS+ already had some non-standard features [hacks] that Mac did not use like encrypting files with different keys based on the data protection level—that APFS provides—so it makes sense to upgrade iOS first, which can readily leverage such functionality, and it not necessarily a direct result of it being the "vision for the future".