Hello,
I really like this idea and I just implemented it. There is now a new field in the catalogue advanced search, so that you can find the coins that were in use in a given year. You can also enter the word "now" there to find the coins that are in use today, i.e. the coins that are not demonetized.
You can also use the keyword "missing" to find the coins for which we are missing the information about the demonetization.
This actually gives us an interesting perspective of the catalog. I tried searching for all Canadian coins that circulate in 2017 and got 1500+ in return. I assume 1 Cent - Victoria KM#1 is still technically a legal tender and theoretically 5 of them can be exchanged for a Nickel at the bank, but should the non-circulating issues really be included in this query results? Also, it gives a somewhat easy way to see which of the truly non-circulating coins haven't been marked as such, e,g, this one.