There is definitely hope, it could turn out to be empty hope but... APFS has a lot to offer Time Machine as the hackery needed to get it to work on JHFS+/HFSX is tomfoolery at this point. At the least APFS has metadata checksums, and adding on an optional csum tree for data is not difficult for Apple to do. They already do COW with APFS so all that's needed is a separate tree for data csums. And then they have snapshots instead of hardlinks; or reflinks instead of hardlinks. I think it'll happen eventually as the deadweight of supporting HFS+ catches up with them.