Cheers, and thanks for asking. :)
> are there any papers on it?
None that I know of, but I have never looked. Hypnosis in general has a hard time being accepted by conventional science (going back to Mesmer and Ben Franklin.)
> the use of hypnosis to create unconscious “hooks” into conscious thought.
Yes, this was literally one of the first things I learned when I started studying and using hypnosis: a binary Boolean signal from my unconscious to my conscious minds (idiosyncratically we (my conscious and unconscious minds) settled on twitch of the right arm shoulder for yes, left for no. Technically it's a trinary signal, with no twitch indicating a "reformulate the query" or "does not compute" response.)
Really, the thing to do is improve communication and report between the unconscious and conscious minds, operating with deliberate cooperation (rather than the ad hoc programming you get from life.) E.g. when I play chess I do not think about the moves, I look at the board and "just know" which move to make. I can actually decide whether to beat someone or lose, and by what degree! (As you can imagine, it makes chess dull.)
> This could be useful if for whatever reason certain features of conscious are not easy to detect (another comment mentioned that it’s harder to get clear signals from the frontal cortex).
Yes, translating and amplifying signals is trivial, your brain does it all the time. However the entire point of having a "conscious mind" is tied up in being easy to detect. The ego is a communication device.
> Then there is the idea of using muscle twitched / GVS as an information channel. It seems hard to get a high bandwidth from this (compared to invasive or EEG-like approaches).
I actually have no clear idea of the bandwidth limits from the unconscious mind to some specific sensor system. Keep in mind that touch typing is already a form of this: the unconscious mind moves the fingers and a stream of text goes into the computer. Achieving that sort of bandwidth should be no problem: set up a binary signal on each finger and an "ACK" on the thumb and you can transmit bytes in parallel, eh? Build something like this "squeezebox" keyboard[1] or a dataglove[2] and use chords from greater bandwidth.
We also have the face, a high-bandwidth output channel, and I have no doubt that a camera (or two) with a simple neural net could be used to train the system to recognize facial tics and expressions. You would have to be a little sophisticated in how you set up the feedback loops: you want to settle on motions that are easy for the face to make and for the NN to recognize. That's kind of a neat thought experiment. (No pun intended.)
I don't doubt that you could get higher bandwidth from implants, I just don't think it's worth the surgery (for able-bodied folk. For people with paralysis it makes more sense.) Not EEG though (I know a neuroscientist who has experience with high density EEG and from what I gather it's just not that great. Like trying to find whales by analyzing surface waves.)
[1] https://peterlyons.com/problog/2021/04/squeezebox-keyboard/
[2] https://en.wikipedia.org/wiki/Dataglove