I use pure coconut peat, perlite +perlite and sphagnum it works well for me only for lowland nepenthes.
For highland nepenthes i use kanuma or akadama for nepenthes with a top dressing of sphagnum moss.
It works better with live spag on top as they like to root in it.\
The only highland nepenthes that have grown well in coconut coir is rigidfolia and species similar.