Hi Jeff, this is a very interesting idea.

At first sight, there's nothing wrong in providing and sharing information about almost anything. So theoretically this idea is great. But I do see some obstacles a) in the execution and b) in the way the information will be received by some readers.

There is a saying that "half-knowledge is worse that no-knowledge". In our case I believe this means the info must be accurate and detailed and it should be read the right way.
Which is near to impossible in my opinion.

Some points:
What if one says he has seen 300 and another says 100 Viceroys listed on ebay, who's opinion would we trust?
And lets say we agree that there were 250 listings of Viceroy Autavias last year, but how many of them were repeated listings of unsold watches?
Were all these Autavias the same?
Is there a huge difference in rarity between cal.11 and cal.12 Viceroys? For example Viceroy Autavias in general might be too common, but at the same time cal.11 Viceroy Autavias could be ultra rare. Or maybe (as an example) there are many Viceroys on the market but most of them are in bad condition and there are very few in good condition so "good condition Viceroys" are rare... etc... you get the point.
It would be right but at the same time misleading to just say that Viceroy Autavias are common. On the other hand if we divide models too much (cal.11 Viceroys, cal.12 Viceroys, good condition Viceroys, etc.) the whole thing would be overwhelming.

Just look at the MOAT and imagine the work that needs to be done for everyone of these models. There are more variations out there than anyone can imagine and for sure there are more variations that the MOAT mentions.

And last but not least, what would be the meaning of this data. Yes, experienced collectors would use it as they should (and with a grin of salt), but it would be too easy for newcomers to misunderstand the meaning of this data. Some may confuse rarity with value, some others may not be able to understand that a little difference can make a watch more rare than another watch although both belong to the same model line... etc. etc.

I imagine new Heuer-lovers going back and forth from ebay to OTD to check rarity, prices and 100% originality. Does this sound like fun?
Thinking of it, I'm happy that I bought my first Heuer because I liked what I saw, without caring too much about rarity, average-market-price and 100% originality.

Maybe I'm just in a bad mood (which, btw, is not very... rare), maybe I can't understand the great value of such a tool... But go ahead and take the first step, it may be worth a try.