I think there's definitely precedent for dope tees in all of these fabrics.
For linen, you've got Acne's Granville and Everlane's womens' tees, plus maybe Our Legacy.
For silk blends, the standby has gotta by Alexander Wang's rayon/silk, which I think would be similar to a modal/silk. And as far as I know, that's one of the most popular lightweight/drapey tees out there. Rick Owens makes a really nice silk blend tee, too.
For pure silk, you've got Rick Owens and Saint Laurent as reference points. From a pure looks perspective, I think SL's silk jersey tees are the best thing on the market right now, though the price is obviously ridiculous.
I think they'd all be fantastic options, and I'll buy into whatever the group decides on. While I know it might be logistically impractical, I'd love to see swatches of the different fabrics, but barring that, I'd guess that they'd all be light and drapey, with a linen blend having a rougher hand and being a bit more structured at first, pure silk being sleek and flowy, and the silk blend somewhere in the middle. And the pure silk is gonna be stupidly expensive...like, over-$100-per-tee expensive (at least that's what I'd expect...)
More important to me, while I'm giving my 2c, is that the fit stays the same or similar to the old bamboo/sorona tees. Part of the reason I love those tees (and own 10 of them) is because of the fabric, but just as much it's because they're the best-fitting tees I've ever worn by a country mile. I've got a very athletic and slim build, and no other tee has ever fit me so well in the sleeves, the shoulders, and the body as WvG. I'd buy tees with that fit in just about any material.
EDIT: Was writing this while the blog post went up. And here I was thinking we wouldn't get swatches. Awesome! All the fabrics look incredible, and I'm totally on board with the U-neck choice. These are going to be killer tees.