How hard would it be to do a calculation to estimate the amount of metabolic activity or autolysis necessary to have a perceptible effect on the taste? If it's the sort of thing you could estimate then you could get an idea of whether or not it's plausible to expect some change.
I dunno. I imagine pretty hard, because there are a ton of different things that can be changed in many different ways. If you're looking at the change in one particular thing (pH, or perhaps even more specifically, the concentration of lactic acid or something) on a known substrate, with a known yeast under known conditions, then most likely you could build that. Some parameters may be really general and insensitive to slight changes (like pH may always go up by about X after Y time, for pretty much any strain of yeast in any wort), but there may be some that aren't. Off the top of my head, I really dunno.
Back when I was doing analytical work for the UW bio department, we'd take a single strain of algae and look for fatty acid composition changes while we changed just one variable. So we'd do a whole series of different pHs, salinities, nitrate concentrations, light/dark cycle changes, temperatures, etc. and try to figure out which knobs we could turn to re-compose their fat content. Some things had little to no effect, while others had large effects and which variables were effective varied from alga to alga. One alga might be real sensitive to salinity changes, and increasing it slightly might cause it to get stressed and produce more storage lipids. Another might not care at all. Some variables were more universal, though. Starving the algae of nitrogen very often (though not without exception) increased the lipid content. And this was all for axenic cultures.
In essence, what I'm saying is that there may be some general rules about how this stuff will evolve with time and other parameters, but there are a ton of parameters to explore and I can't say for sure which parameters will matter and how. I do suspect that since we see the same basic ecological progression occur in pretty much any spontaneous fermentation that some fairly general rules might be established, though probably more qualitatively than quantitatively.
Here's just about the best review article on this I've seen, though it's been a while since I read through it.
And of course there's this too. I'm curious more about whether pH can really change enough to be noticed, I very much believe that someone could think it's happened regardless of whether it really has.
Yeah, that's definitely a much easier question to answer. Unfortunately most of the evidence I've seen for changing pH with aging has been anecdotal sensory reports.
EDIT: I haven't searched for this yet, but Milk the Funk might have some more formal pH measurements of their beers as they age. Not quite the formal PR literature, but it'd be a hell of a lot better than someone saying "I feel like this beer tastes less sour than the last time I had it four years ago" is.