Also, just noticed that the UI of Wasteland (1988)  in that video looked hugely like Infocom's Battletech: The Crescent Hawk's Inception (1988)  but I can find no documented link or engine reference.
I also remember programming my first games (space invader clones) in BASIC on the A3000 (and the A3020s we had at school) - fun times.
This would make it really easy to do something like duplicate a line while changing some things, just move the copy cursor to the line/variable/thing you wanted to paste and modify, then hold the copy key until you got to where you had to change something (at your current location the characters from the other line would appear), type what you wanted, then back to the copy key for the rest of the line
Seeing my best friend at the time use it it seemed really cool, some days I think of trying to write a minor mode for emacs that lets you do that...
Interesting tidbit: it matched the data on the screen with the font in graphics mode, which meant that if your graphics intersected anywhere with text you wanted to copy that it stopped copying on corrupted characters. There was too little memory in those machines to keep a 'backup copy' of what was in the character cells of the screen, so the copy key function had to recover the screen contents directly.
You can see the keyboard here, the copy key is bottom row, rightmost key.
Really surprised it didn't catch on in other editors, I wonder if it could be done in emacs by having a command that copies a char from mark to point and moves them both right, as well as a different cursor to put in mark, since you can already exchange point and mark it seems this should make this functionality feasible
Edit: It was Nevyron: https://youtu.be/jOwhIlMoZZs
The intro music still sets the spine tingling :)
Later when encountering an Apricot PC running Aldus Pagemaker on Windows (Or GEM? Can't remember now) I recognised it as the same kind of thing as the Archimedes. As was the funny little monochrome Macintosh.
I'm a bit old for the Sinclair thing.
Some technical details...
The A310s were built like tanks and were very fast for the time... unless you wanted to do floating point calculations. You could get a podule with a floating point extension unit on it.
I've actually been considering getting one for my kids to play with - the simplicity of having basic right there and having physical disks gives a great way to explore what's really going on.
BASIC on an Acorn was my introduction to programming.
I was aware that the machine was very expensive. All games played better than on my friends' computers, and it could even play video and render 3d models (in 1991!) so my friends pestered their parents, but it was too expensive. Ours were all second hand, my dad taught students how to use them, but couldn't afford a new one.
There actually was an elastic band in the disk drive: I remember replacing it twice in my dad's PCW9512 when it wore out.