I've seen plastic nails use in foam-core construction, but not in solid woods. If I were going to experiment, I would start out with 40% glass type 6 nylon, but this is only a guess. I'm sure that there are other posters who could shed a better quality of light on this subject.
I have seen some testing done many years ago, so I have forgotten a lot of the details, but as I recall 50% GF 66 was best, but there was not much difference between 6 and 6.6 at 50% glass. The 6 is somewhat easier to mould.
50% GF 6 is also currently used for plasterboard screws.
If it will bear the cost, 50% long glass fibre 6.6 will give even better performance, but it is expensive, and it requires some care with machine and mould details.
I have seen plastics nails driven through 3mm aluminium sheet as a demo. The material was a polyarylamide (trade name Ixef, made by Solvay). I think it had 60% glass fibre reinforcing. It's not cheap compared to GF PA6.6. Other materials similar are Grivory (made by EMS Chemie), and PPA (made by various)