quoting my old comments, in case github dies next week or people just prefer comment sections over anubis "catgirls":

It is my understanding that Sybil attack mitigation via fidelity bonds as described in the above text would reduce available liquidity.

It would be preferable for a system that allows the relevant coin-age accumulation to proceed in isometric parallel to a coin's availability. I don't recall ever making a formal writeup of the idea to factor accumulated coin-age into the taker algorithm for counterparty selection, although this has been discussed on IRC. This idea has the advantage of not requiring any modification of the existing protocol while tacitly acknowledging that certain participants choose to allocate their liquidity in a manner other than a single lump sum, and the disadvantage of requiring the takers to burn their utxo commitments at a greater rate.

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clarifications after IRC discussion of the above:

• One such a system would be that takers validating the offered liquidity would consider utxos as probabilisticially invalid, according to the number of confirmations on each utxo. This would reduce reuse of recently active liquidity, and prioritize liquidity's participation according to properties of the specific coins in question, instead of associating the participating liquidity with other coins.
• coin-age, also known as bitcoin-days, is the bilinear product of an unspent transaction output's value, and the number of confirmations on the transaction from which it originates.
• proceed in isometric parallel coin-age can accumulate in a linear manner, although arguably the metric used by takers should increase superlinearly in confirmations, so that takers would express a strong preference for joining with older coins
• a coin's availability is the inclusion of a given utxo in the liquidity pool that can participate in a coinjoin at the given moment, i.e., presence in a hot wallet attached to a live liquidity provider.

tl;dr: The most significant unspoken question is whether "liquidity" can even be defined without some level of de-anonymization of the UTXO set; my idea was to avoid violating fungibility in principle, by having takers consider all available counterparties a single Sybil swarm, and selecting the UTXOs that produce the best resulting overall graph, when considering the iterated result.

bit of a mouthful