As previously said, welcome back to HB!
Your idea of having an online calculator that can estimate the rate of coffee staling in a freezer is interesting and has merit. I would caution however that our "molecular" understanding of what is actually going on with frozen roasted coffee, particularly as it applies to what we call "staling" in coffee stored at room temperature, is somewhat limited. We know that freezing "works." We also know that oxidation is slowed down with reduction in temperature. We know that coffee degasses as it ages, and presumably this has some relationship to the "staling" process. We know there are oils in roasted coffee that are in a liquid state at room temperature and that presumably are in a solid state when frozen. What we don't know is how exactly we can quantify this thing we call "staling," because we don't know that oxidation and degassing, which may be quantifiable vis-a-vis changes in storage temperature, are the only things going on that relate to staling.
Unlike some here, I freeze my roasted coffee immediately after roasting. I have not necessarily noticed an obvious correlation between freezer temperature and the extent to which plastic storage bags "pump up" over time. Even if I did, I think it would be a bit presumptive to assume that the extent to which the bag puffs up correlates exactly with the rate of what we call staling. There may be other factors at play that explain limited degassing in the frozen bag of coffee, such as small, unrecognized variations in roast profile, degree of roast, or the green coffee itself that was roasted before freezing.
Having a rough idea of how quickly your frozen coffee will "stale" is of course a good thing. From a practical standpoint, I would encourage people to freeze as quickly after roasting as possible, to use the coldest freezer they have available, and to freeze in portions that can easily be consumed within a 3 or 4 day window. There is obvious benefit in having a stash of coffee in the freezer, as it does allow you to have more different types of coffee available for use at a given time, and to time shift your roasting sessions. At the same time, beyond a certain point, the convenience factor and availability of several coffees simultaneously is no longer benefited once one has a certain amount of coffee in the freezer. So, it is probably better to keep your frozen stash down to the point where you don't have frozen coffee that is older than several months post roast. Following these above guidelines should allow one to end up with the best possible results from the coffee that one freezes.
As I have posted before, I find that most coffees have a fairly brief period after roasting where they show the best, for espresso. As a result, I'm tending to leave less coffee of any particular type out after a roast session, and to freeze more of the roast product of each session, in small containers (most typically ~150 to 180g, in my own case). By using this strategy I find that I can consume most of my coffee at its peak, rather than watching it go downhill as I consume it.
What, me worry?
Alfred E. Neuman, 1955