I am happy that things have converged over time to a single, truly versatile multi-bus capable port (USB-C/Thunderbolt 3) ... however, the vendors IMHO should be legally bound to supply down-converters for all the peripherals that used the older buses for the next 10 years, transitively for 2 generations of buses.
If USB-C supports bus 'X', then there should be inexpensive and easy to purchase down-converters from USB-C to 'X'. If Bus 'X' replaced bus 'Y' in the last 10 years then there should be a down-converter available from bus 'X' to 'Y'.
One problematic example is Firewire.. Apple used to make Thunderbolt-2-to-Firewire800 dongles, but they stopped and now they're rare as hens' teeth and ungodly-expensive.
They still sell Thunderbolt-3-to-2 dongles, but how long will they keep selling those?
Oh, and while I'm wishing for ponies, the drivers/specifications for all such adapters should be open-source and royalty-free.