IPv6: ehh, maybe, it was an issue but not the primary one
upload speeds: no (most Not Computer People don't realize there are multiple numbers involved in network speeds at all)
eventual sync: ehh. probably need both, but syncthing is painfully underused as is and it's, like, the minimum effort self hosting thing.
IMO it was always primarily a marketing problem. If people had decided these were the things they wanted, they would've pushed for the technologies that made them easier.
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