I'd suggest a quest that's mostly linear, as some of you suggested, with a different feature in each room (item, shop, warp, secret, tiered secret, ...). There are literally hundreds of features I could think of.
Then someone could write a tutorial that explains for each screen how it was made, sort of a zquest screen-by-screen tutorial. The first screens would be simple things (how to place combos) and in the end, if we're lucky, you'd have a custom boss... Of course the tutorial quest would be unpassworded so you can play the screen through, read the tutorial and look at it in zquest.
I would be quite interested in helping to make such a tutorial, be it in zquest or article-writing. I've done a mini-tutorial on flags, something in the same style but on a much larger scale is what I'm suggesting.
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