I doubt I could claim credit for applying the techniqe of using a cross-stitch "X" pattern to build an elaborate design in Adobe Illustrator, but I came up with the idea on my own and developed it through experimentation.
Here's an inset portion, showing a two-color stitch pattern:Once you have a few patterns, you can start to replicate them and lay them out into a larger work. Here is a completed rushnyk from a design I copied:
There's a really cool trick you can do in Illustrator, where you can take something you've designed and make it into a pattern brush. The pattern brush can then be applied to a vector shape like a line, rectangle or circle. The basic square of this pattern lends itself particularly to a rectangle, because you can designate a specific design to be a corner piece in your brush pattern.
To do this, I first stripped away the outer zig-zag border. Here's what the replicated squares would look like in a corner pattern:Once the pattern brush is complete, you can begin applying it. Here is a circle within a square with the rushnyk brush pattern applied:
Note that you can change the stroke. The circle is one-half the stroke of the square. The only problem with creating these elaborate designs is that you can run out of memory when you try something large based upon an elaborate design.