@madhatter, yes, the proposed syntax of "<query>??" to invoke the Assistant is not adding new functionality to Kagi, since it is equivalent to using the "!assistant" bang. However, I believe it is a "natural" extension of the existing syntax of "<query>?" to produce a Quick Answer, and helps to make the use of the product a bit more friction-free.
In brief, the proposed concept is that "<query>?" gives the user a Quick Answer, while "<query>??" delivers a more detailed answer from the Assistant.