The textile seats are fantastic. They look really great in person, and have held up very well. We have a few Teslas in our building and one wishes he got the textile seats due to the wear on his leather seats.
They're a nicely-textured fabric in the center with small patches of synthetic leather for looks. It feels much like the leather in Tesla's original seats. They chose a very nice synthetic. The combo is pretty grippy, so you slide around less in the seat without the larger bolsters of the next-gen seats.
Not sure what you mean about the "obligatory upgrade to leather or vegan", though. The "vegan" option is the base textile seats + a special custom steering wheel wrapped in the same synthetic leather as the textile seat inserts. The standard install is a leather wheel, even with the textile seats. That's the only difference.