I would love to have something like TC Electronic has. In their tuner they had this polyphonice tuning, that can detect things within a chord, or you strum all string simultaneously. This method has been done at a company called Jam Origin, a product called MIDI guitar. It tracks polyphonically without latency, without need for a hex pickup and can drive and run most software synth plugins. As well as automatically write down a midi file from what you’re playing on guitar.
Now TC has released a few pedals with this “system” or “process” in. One of the most remarkable one is their “Sub’n’Up” which is a perfect pitch tracking algorithm, for mimicking both an octave down and an octave up. Especially when used octave up, it tracks it and produces a sound closest to 12 string guitar, and especially 8 string bass (double courses) that I’ve heard. Even when strumming chords. It doesn’t really do the 12 string, but it produces octaves higher still, on the B and E string which is unison anyway on a 12 string. The other pedal is the tuner thing.
So something that can track/pitch/trigger chords properly without latency and “guess it right” to produce 8 string basses, 12 string guitars sound. Polyphonically. Todays octavers and pitch shifters – even though it’s Eventide – can’t track chords properly yet and put an octave up for each note. Of course, it should do one octave down to with chords, but chords are not generally played that low, it just becomes muddy anyway, even if you play chords down low on a regular bass.