Here’s something to consider while we are all stuck at home. Seeing a representative of all ~250 bird families is eminently achievable for those with the time, money and inclination. Do enough birding tours to the right areas and you can get them all. A second trip for some families may be required if you are unlucky. You can see more information about how to do it at http://www.tropicalbirding.com/wp-content/uploads/articles/Its-A-Family-Affair-Woods-Barnes.pdf (albeit that’s slightly out of date now). It would require a couple of trips to most continents, visits to other well known biodiversity hotspots such as New Guinea, Borneo, Madagascar and New Zealand, and then a few more targeted trips would be needed, to New Caledonia, Sulawesi, Cuba, the Dominican Republic and Puerto Rico.
But what about seeing a representative of every mammal family? Is it achievable? Where would you have to go, and what would be the hardest families? A look down Jon’s life list suggests there are about fifteen families he’s missing, based on his checklist. Some of them seem gettable if that’s your focus (e.g. Feathertailed Gliders, Monito del Monte and Aye-aye). Others could take a lot of time (Pygmy Right Whale and Pacarana?). Are Mole Rats and Marsupial Moles the dealstoppers for the average mammal watcher?
A good visual guide to mammal families, albeit using different taxonomy, is at htps://www.lynxeds.info/sites/default/files/pdfs/Lynx%20Edicions_Families%20HMW%20Volumes.pdf