The thing to remember with rope rigging is that if it rubs against a sharp surface, it can be cut. This is easier to do when under tension too.

I wouldn't want something that can be easily cut holding my mast up, whether it's stronger than stainless steel or not. If there were a couple of stays, so that there were backups should one fail, then that would be a different story.

Stainless steel is proven to work on our size boats, going with lighter stays isn't going to improve your performance significantly, and probably not even proportionally with the risk of dropping the rig.

Using rope for your trapeze is pretty low risk (low "cost" of failure (at worst you fall in the water) and low chance of it happening (particularly if you inspect the stays regularly and replace if worn)). This is how planes stay in the air, use lighter structures (with finer safety factors) but inspect them regularly for problems, repairing when necessary.

The risk associated with falling in the water is another matter. If you are inland racing with rescue boats around, the risk is low. If you are sailing in the ocean without rescue boats, the risk is high.

Since the risk is to yourself as user of the boat, you have to weigh up the options.