It is "remotely" possible, if the printer has a USB hub built in so that it can pass through devices to your computer. Yes they will be connected together but they will not act as a single device, you will have to install drivers and software for both devices for them to work. You will also loose any simple "copy" functionality that the all-in-one device has.
Most of the mutifunction devices actually act this way to begin with, the thing that "binds" the devices together is the actual software that is supplied by the manufacturer, both onboard the device and in the computer. As far as the computer is concerned they usually are separate devices and when the computer tries to "copy" something then it will scan it and then print it rather than use some mysterious built in function.
A printer is a completely dumb device, as is a scanner. Neither of them need any of the processing power or bandwidth that a device like a router has. Sure they can run an IP stack so they have a webpage and work on a network and have USB support, but that functionality is available on the smallest of microcontrollers these days and doesn't even need a "full featured" OS like Linux. Chances are it is something along the lines of FreeRTOS or an in-house equivalent.
The scan button on an all-in-one printer though will be a built in routine that simply runs the scan routine and rather than send data to the computer will then pump it back out to the printer function. Because the microcontroller knows the formats expected by the scanner and printer it can do the conversion without having to understand the finer intricacies of several hundred subtly different types of USB scanner (with or without document feeder) which would need a more powerful controller and a full operating system.
What that means is that printers don't support scanners because generally they don't need to until they have one built in and vice versa.
This is generally motivated by cost. Full SoCs that can run Linux used to cost anywhere from $10 each and going up, though they have been getting cheaper, a simple microcontroller that is simply capable of doing the job of feeding some already formatted data from a windows print driver over usb to a print head or copying data off of a scanner in the opposite direction could be less than $1 each for production quantities. It might be that one day we get devices that can all support each other happily but it is still always going to be cheaper to go for "good enough" rather than "good for everything".