> What “modern platform” would you suggest?

I can't really think of a suitable one TBH; Python's completely out of the running, Java and C# have a lot of unnecessary (for this goal) boilerplate, Pascal is not a bad choice.

Maybe Javascript? The books can then instruct "type this into an HTML file".

In my mind, a more modern platform would be a simulated one that has its own machine language (byte-code compiled, perhaps) so that these books, which take you all the way into machine language, would make sense.

Lua/Love2D?