My take is that it is exceedingly difficult to amplify and pass an audio signal
flawlessly, in a manner that preserves every possible nuance of the original signal, without adding anything. It is much easier to NOT pass it with fidelity. The entire domain of "distortion" is an exercise in the myriad of ways there are to
not pass a signal without altering it.
Consider the number of ways there are to botch a grilled-cheese sandwich. You could burn it. You could stick compromising ingredients in it. You could try and make it sideways. You could try and boil it. All of those are ways to ruin a grilled-cheese sandwich. The same is true of distortion. Diodes and misbiasing transistors are certainly some of the ways, but they aren't the
only ones. So there will inevitably be ways of producing musically interesting distortion that have not been used before. Ultimately it becomes a matter of whether the means of producing it is:
- bulky, power-consuming, or otherwise inconvenient for the user or retailer
- consistent in a manner that allows for predictable application
- available at a pricepoint that can sustain a market and profit for the maker
If you can hit those marks, then any means of producing it is fair game. Now, whether the tonal product is audibly
different enough from whatever else is out there - and there is a LOT "out there" over the past 50 years - is a whole other thing.