These are very jnteresting design elements, I can see why you’re drawn to them.
The second one is easier to work out I think as the needle size changes like a horizontal stripe so all stitches are worked onto the new needle and the stitch count altered for gauge as the piece is worked. I can see areas where there is a decrease in stitch count between the smaller stitches and the larger so whilst one might want a sleeve to have an increase in size going up from cuff to shoulder, this wouldn’t necessarily mean an increase in stitch count but could mean a decrease in stitch count.
I’ve seen patterns where the stitch size/gauge is not so obviously changing and different size needles are used in the same way to shape the body of a sweater instead of using increases and decreases in stitch count. I have never made one myself but think it an interesting construction and I like this cable example with the obvious gauge change, it’s great.
Working some swatches with different needles to decide which you like would be relatively easy, then working out the size and stitch count from these which I think is the harder part. Each section might need to be gauge tested for the cables to look right and measure as needed for a good fit. Worth the work though, it’s a stunner!
My first thought about the sleeves on the colourful sweater were that you had a good idea about working them like intarsia, but changing needle size across the row. I think there could be a possible ladder problem between needles, each different size would need to stay on its own size needle - well many people work with dpns and manage to avoid ladders between needles, so why not? Probably only m hat would struggle.
Again, I like the design of it, great use of gauge variation. I wonder if 2 weights could be used with the finer weight for the small gauge, a heavier weight for the middle gauge and then 2 strands of the finer weight to make the chunkier weight gauge.
Or 1 strand, 2 strands, 3 strands - easier to purchase a single weight in a single colour so you don’t have dye batch problems?
Another way to work it could be in narrow strips seamed together.
Thanks for sharing. Now I want to make one of these too!