I’d like to offer another angle on this issue that ties back to the incentive mismatch raised earlier.
Routing nodes are naturally incentivized to minimize latency. Holding an HTLC slot longer than necessary can reduce their capacity to forward other payments and may lead to lost fee revenue. Nodes that don’t see heavy traffic may also see little reason to batch, unless it’s adaptive and only used when demand is high. On top of that, longer-held HTLCs increase commitment transaction weight and could raise the cost of force closures. This has all been mentioned already.
From their perspective, there’s no benefit in adding delay to HTLCs. So why would they, given these downsides?
Even if we try to encourage delay-based privacy features, the economically dominant nodes may strip them out to keep latency as low as possible. This is rational behavior under current incentives.
Now suppose the network converges on coarse-grained hold times, say all nodes advertise 300 ms.
In that environment, a node that wants to introduce privacy-preserving delays at its own cost has no way to stand out. The coarseness of the hold time field makes it impossible to signal variability or randomness to the sender. Every node appears the same, even if some are doing extra work.
In that sense, coarse-grained hold times may actually discourage privacy improvements. They flatten the signal space and remove the ability for privacy-oriented nodes to differentiate themselves from latency-optimized ones.