There are some hard parts (e.g. I don't expect mechanical compatibility across appliances anytime soon) and easy parts (charging). There's really nothing fancy

There are some hard parts (e.g. I don't expect mechanical compatibility across appliances anytime soon) and easy parts (charging). There's really nothing fancy about the chargers that all the appliances use. USB PD isn't designed for smartphone batteries, it can power lots of things, including laptops, monitors, soldering irons, large power banks. Appliances' batteries are hardly any different from a power bank. There is no "battery smarts" in the charger itself, it just gives juice to a charge controller located by the battery. I don't know if it scales enough to be usable for 48V appliances, but a lot of stuff could be powered by a common interface (and, conversely, most large batteries could easily double as a power bank, and they indeed do if you just attach the right electronics downstream of it; having this built-in would be an interesting step).