I prefer a graduated scheme, where long-running, active accounts can have lower sybil fees and newer, less active accounts have higher fees (after some grace period for newbies).
Honestly, though, I'm pretty content paying a 30% tax to have access to this service right now. There's nothing else like it on the internet as far as I can tell
To make this feature sybil resistant, SN takes 30% of zaps and re-distributes them to territory founders and the SN community as part of the daily rewards.