Beautiful. Another approach to visualizing the discovery of elements would be a "time travel" feature, where you see a timeline with just years below the table and can click on a year to see how the table looked that year.
You've added something that dims elements in years before they were officially discovered; but this is not “what the periodic table looked like at the time”. When I was a child, the periodic table had element names hahnium and kurchatovium on it. This is probably not easy to implement because many elements had multiple names between the US and USSR and they were not internationally standardized until 1997 (long after the fall of the USSR).
