[2020] Can't buy just the Grail Knight cosmetic upgrade.

It's a limitation in how the Steam store infrastructure works, as opposed to a mistake on our part. The cosmetic upgrade has to be tied to the base career in some capacity to reduce (or remove outright) cases where players purchase the upgrade on it's own for themselves. The only way to do this at present is to bundle it, and not give it it's own specific store front where it can be purchased in isolation. The result is that it can't be gifted, which is hugely unfortunate, but saves a totally more unpleasant wave of confusion from players who mistakingly purchase an upgrade to a product they do not own.