You're going to need Walter or Brian to explain the technical details. I think that there could be a path through the weeds to have a modern tablet device drive an autopilot, but I'm not clever enough to know that for sure.
I know very little about how USB works so take everything after this comma with a boulder of salt, but what I think I know is that a USB device can be either a "host" or a "peripheral". In the olden days, phones and tablets were constrained by design to only be peripherals, but they'd need to act as a host to drive a peripheral system like an autopilot. There were adapters (look up "USB On the Go" if you're curious) that could enable a peripheral device to act as a host, but I've never actually seen one of those utilized.
Today, with USB-C, I think the host vs. peripheral roles are negotiated when the connection is established. It seems like theoretically you could build a reasonably-priced USB-to-serial cable adapter to enable a tablet to control an autopilot similar to how the 7xx devices work, but again, I'm a total neophyte on this topic so there may be showstopper reasons why that just can't be done, or is not practical.
I'm pretty sure I asked Walter about this 2-3 years ago and he said it was not practical. I think that might have been before USB-C was ubiquitous, though, so I'm not sure if anything might have changed since then.