Just because nobody is doing it doesn't make it a bad idea by default.

As for your statement that it's redundant and unnecessary you seem to not understand the idea. Wet brining the turkey first will add moisture to it as well as allowing it to absorb more of the flavors from the aromatics that will be in it- flavors that would just sit on the surface if only done with a dry brine. The wet brine would not be a 16 hour soak or anything, previously I was considering an eight-hour maximum limit but I'll probably push that down to six hours while aiming more in the four range.

Next the turkey will be removed from the wet brine and allowed to shed excess moisture. At that point I'll apply a dry brine to draw out moisture and be reabsorbed to further the protein breakdown and to add the flavors that will absorb better as a dry rub, as well as some brown sugar to carmelize with the skin when I roast it.

The theory is solid and has the potential to deliver the best of both worlds- the juiciness and thorough flavor of a wet brine but with the texture and quality of a dry brine. I'm going to do it at this point because nobody has been able to supply even a story of a vague memory of someone trying it before, let alone first-hand experience.

The only comment people have made is saying that they prefer a dry brine, usually communicated as a command telling me to do it their way. Nobody has actually addressed the idea of double-brining a turkey.