I'm a bit surprised that there hasn't been much discussion about possible uses of steel thistle silk, even with the cost problem. IIRC many of the early balloons used silk to keep the weight down.
One item worth considering: at present, some groups are trying out parasails to reduce fuel consumption when the wind conditions are right. Why couldn't someone who is checking out the best uses for STS in sails think of a steerable spinnaker, which is basically what a parasail is. Also, a parasail powered ship would have less leverage from the sails, therefore less heeling of the hull. Possibly someone with sailing understanding could outline the possibilities?
When the point of heavier than air flying craft is reached, it would be good for cloth covered wings. At present some small slow aircraft are using parasails instead of wings. Even before that, some form of dirigible or zeppelin design could make good use of it.
No mention has been made of ropes using that material - it might be a bit before the cost is low enough to allow that, but there could be places where the extra strength would be worth the higher cost.
Other ideas?
, would be for cordage (ropes). Nothing has been said about its resilience or stretching, but in the tech era Safehold is currently in, there is an enormous usage of all matters of rope and, if it is like some of the 'modern' synthetics, it is a non-proscribed revolution on its own!