I do have a tendency towards overengineering and it's possible that is coming through, but equally I wouldn't underestimate the requirements.
One thing that is giving me a moment's pause is when I think of a couple of bookcases I picked up from Argos perhaps ten years for somewhere around £40 each. Make no mistake, these are absolute crap but they have done the job.
They're 6' tall, 12mm chipboard, one fixed shelf halfway up, the others are repositionable. The one in my bedroom is full (see photo) and while some of the shelves are sagging a bit the unit as a whole seems solid enough. The joints are simply screwed butt joints. The screws are fairly long (three or maybe even four inch) - accurately drilling pilot holes that deep is easy for factory processes. It's a bit trickier with basic tools but I'd put it in headscratcher territory rather than impossible.
Crucial though is the bracing to keep everything square. There is a small kickboard at the front but that's probably only 3". There is however a full back. It is only a hardboard panel pinned on but even hardboard can impart a good deal of strength used like that, with the load travelling along rather than through the surface. As I recall before the back went on those bookcases didn't inspire a lot of confidence and were decidedly wobbly even when empty.