Re: As an aside...
> It feels *wrong* to use a Raspberry Pi as a video co-processor for a 6502...
I know what you mean and I agree.
OTOH, the £3 Pi Pico doesn't seem quite so crazy... although it does need external circuitry to do that.
TBH this is how modern phones and laptops work. It's easier to implement various networking stacks in software on an embedded Arm core than it is to design *and debug* hardware to do it.
So, an iPhone has something like a dozen+ Arm cores, some running Bluetooth, some running Wifi, some controlling the screen, some controlling the storage. Even a cheap tiny SD card contains an Arm core running the actual storage, and multiplexing the data over the card's few I/O lines. As an exercise, people have installed Linux onto the Arm in SD cards, as well as onto the Arm on SATA hard disk controllers.
Your phone doesn't contain an Arm processor. It contains a cluster of clusters of Arm cores, all talking over different interlinks of different speeds.
It does in fact contain an internet: a network of networks, working together to let you connect to the planetary internet.