I should say - The guy who created Black 2.0 has demonstrated you can dye with it. But it isn't really any more black than most black shirts you get retail, to get it really black you need to paint it onto the shirt and that doesn't really get you anywhere, except a very stiff shirt with mediocre paint coverage as it wears off. I'm thinking of trying something like steaming the base shirt extensively and then dying it in a hot mixture of Black 2.0 thinned with water. That might get it deep into the fibers. Doing that two or three times might be what it takes.
Ostensibly - a company has made a blacker t-shirt (Viperblack), but having seen it, I'm not convinced it's any more "black". One thing to consider if you want to make a "Blacker than Black" cloak is stage velvet - ShowTex Shakespeare or Goethe Velvet in "Ultra Black" were certified by NASA as the "blackest fabric". And they are pretty damn black, but they are not matte black (like Vanta or Black 2.0).