Hi, vinegar manufacturer here. I have not heard of this and I think there may be some confusion about making "leather" with a kombucha scoby. First, leather is from cow hide and the structural proteins that make up leather are collagens. Kombucha scoby is actually just a mother of vinegar (kombucha is basically dilute vinegar from a sugary tea base) which is made of cellulose as you state below.
There is actually a large amount of research being done on using mother of vinegar cellulose has a possible feedstock for paper production, mostly using Komagaetaeibacter xylinus (also known as Gluconacetobacter xylinus or Acetobacter xylinus in old books). This is a very productive cellulose producing strain and they try to have it make cellulose using a glucose feedstock instead of alcohol (as in vinegar production) since it is less expensive. The cost and quality haven't quite gotten there yet though.