David Chalmers presents different options of idealism to approach the mind-body problem in his article, and his suggestions got me thinking.
He presents ways of taking a sort of objective-idealism panpsychism that suggests that the ideal substances are not only present in relation to the mind-body problem itself, but to all of nature, kind of like physical particles (admittedly, he's far from the first to present this idea, but he presents it very elegantly). If we take this approach, that those seemingly unobservable substances are in a way affecting our world (something like Copenhagen interpretation of QM, or maybe it only affects us, the observing part) like physical particles, then we may ask - can they be quantifiable?
It might be difficult, if not impossible, to quantify something that we really not sure if we can even observe. But the history of physics teaches us it can indeed happen (Galileo famously said that he first theorizing then does the experiment, so while we won't exactly have the experiment part, we can have the theory part).
Moreover, if we assume that those ideal substances have open causal effects (as in, they're not in a closed system as suggested by dualism, but are actually affecting the physical world) - we might even be able to come up with experimental ideas. Although experimentation isn't exactly necessary, as String Theory had lived on for some time now without having any observable confirmations (and the idea that it can even have is controversial).
So, has any philosopher touched this subject (preferably someone from at least the last century)? Is the idea of theorizing quantifiability of "mental substances" worth exploring?