From what I've been able to find out, with relative certainty, is that the material is called Power Twill and none of the customizers in our hobby have access to it. What I don't know 100% for sure, is if it is a Nike creation they're keeping behind nuclear launch codes or if it's something more rare they decided to use and have agreements with suppliers to only sell it to them or team customizers for game jerseys only. It is softer, thinner and lighter and I must admit, kinda nice. I hope it's an alternative to any thoughts of going to everything pressed on like the IIHF has pretty much done.
For the Mariners City Connect and ASG authentic jerseys I have, this is the material on the front script and also on names and numbers for authentic player jerseys sold on MLB Shop and in team stores (for teams using it so far). Doesn't help people with blank jerseys though. I did contact the Mariners on-field customizer a while back and they told me only replica names and numbers can be put on my City Connect authentic jersey if I send it to them.
I can't see MLB going the NFL and NBA route, where there just aren't any blank jerseys sold at retail. What I do think is coming though, is that Nike will basically make it impossible to get an authentic jersey with accurate fonts, colours and materials for names and numbers, unless you buy through MLB Shop at their stupidly-inflated prices. Another thing that appear to be the case is that ALL MLB teams will be wearing perforated numbers next year, which is an even bigger pain in the sphincter for customizers who hope to replicate whatever is coming.
For now, I'm playing the patience game with my two jerseys and when (hopefully) I finally get them done properly, that is probably it for me with MLB Nike jerseys.