Mycelium is neat, but last time I heard of it the problem was far, far too low manufacturing throughput.

I don't think anyone would even consider marketing that as "vegan leather", as doing so would mean putting you in the same bucket as cheap-as-dirt polyurethane (which is what regular "vegan leather" is), at an astronomically higher price. You'd pick a new term to differentiate.

I vote for "shroomskin".