Here in Central Texas we have lots of agave and I walk past a wild stand often, but apparently the juices are caustic from the field guides I’ve looked at. An idea came to me from something I read some years back about how some modern Indians leach the tannins from acorns by putting them in a nylon hose and hanging it in the toilet tank and in a few days of flushes by the family they are ready.
Seems like that could work pretty well for retting certain types of cordage like agave and with agave you might have the added bonus of the saponins helping keep the toilet clean, I’ll have to try that out.