Cryptonote can't encourage too much use with zero transaction fees, because it can't accept the scaling that can come with it.

I believe Zerocash has similar scaling issues. DarkCoin (and CoinJoin) has the simultaneity problem that fights scaling because to mix you need someone else who wants to mix with you at the same denominations at the same time (not mention being either theoretically defeated with jamming and/or Sybil attack on masternodes) and to perform this meeting with scaling you need global coherence on submitted txs which means either centralization (synchronicity) or no scaling.