I can see how that should depend, at least to some extent, on how good AS macs turn out to be in terms of speed, buttery life, aesthetics, and the like, as well as how well popular apps will be supported and optimized. But I tend to think that these factors are not that important. Of course, if AS macs fail to meet the majority's expectations quite miserably to the extent that some major 3rd party apps are unusable, the value of the current 16" MBP could appreciate rather than go down. Or if the transition turns out to be a huge success from the get go, your 16" mac's value may drop sharply. But I would say these two extreme cases are rather unlikely. If AS macs happen to be just very good or poor, I don't think the majority will care. After all, your average user doesn't know or care what this transition means.
A much more important, or perhaps the single most important, factor would be the prices of the AS macs. Everyone understands what "price" means, and it matters a lot to pretty much everyone. Although the prices are nearly impossible to predict, those new completely redesigned machines won't be cheap. So, assuming Apple continues to charge us the way they usually do, I would guess your mac's resale value will be all right, if not great.
16" MBP is a great machine as it is, and if its resale value drops a lot when AS comes, it means the transition must be a great success, which I hope will happen anyway.