[tomkinstinch]

Yes, like us, fungi are opisthokonts, but where collagen is the mammalian structural protein used for making leather, fungal hyphae are principally comprised of chitin—structurally closer to the polysaccharide cellulose of the mentioned "kombucha leather" than to the collagen protein. Collagen is present in fungi in certain edge cases, but bulk mycelium is mostly chitin. This is speculation, but leather made from chitin may actually be a bit stronger than animal leather made from collagen. Maybe closer to keratin in strength? (Interestingly, keratin is chemically cleaved in hides during leather production--not entirely sure why, to enhance flexibility and allow access to the collagen fibers?). Agreed about fungi being easier to engineer. As you point out, endogenous expression of dyes in hyphae for different colors of mycelial leather is compelling. GFP would be cool too for the rave and nightclub crowd.

The Quorn meat analogue[1] is another product made from compressed mycelium. I've had "chicken" nuggets made from it. They're...not bad, but as far as mycelial structures go I prefer mushrooms.

1. http://www.misac.org.uk/PDFs/MiSAC_Briefings_1.pdf