It would be interesting to scale this design up. Not necessarily in terms of velocity--supersonic velocity for a large trebuchet munition isn't necessarily desirable. What I mean specifically is scaling up the multi-revolution arm and sling release technology to be capable of launching a ~1 ton projectile.

Could it be done reliably with traditional construction techniques (wood, treenails, lashings, minimal metal hardware)?

AFAIK these are innovations that were not explored historically. It would be interesting to see if they would have been viable. It seems like you could probably achieve a lot more downrange energy using the same amount of materials this way.