Thank you for sharing about https://www.oldmapsonline.org/
I didn't know about it and it's a fantastic resource.
I'm not sure how Numista could be integrated in their maps. I don't think it would make sense to show coins directly on the map, like they do for people and battles.
Coins are actually associated to 2 locations: the issuer and the mint. Issuers are similar to the “Regions” which they already have. Are you suggesting showing mints from the Numista database as a 5th tab after “Regions”, “Rulers”, “People” and “Battle”?
We could also think about showing coin hoards and findspots, but we have very few hoard data on Numista for the moment.
I'm not sure I understand either you suggestion do integrate their maps on Numista. Do you mean showing the maps on the search results page of coins of an issuer? Or on the collection dashboard? How would it look like?