I'm a male currently using a clamshell spinner. I was skeptical when I bought it, but that's all Costco was offering when I bought it, so I gave it a try and like it. I'm also a big coffee drinker.

So my thoughts on the cup holder...

First, even though I usually walk with my spinner on 4 wheels, I do also pull it on 2 wheels sometimes - up ramps, on carpeting, or when running. Having the cupholder by the handle means that when I tilt to use it as a 2 wheel bag, my coffee pours out.

Second, the time the spinner design is most useful is for the too-long walks down the plane aisle to my coach seat. The boarding process is also when a cup holder might be most useful, as I'm also juggling my phone and/or boarding pass, and whatever other food, newspaper, etc I may be bringing on. But when I trun the spinner sideways to push down the aisle, the cupholder sticking out makes it too wide or risks the coffee hitting the rows of seats I walk past.

If I'm having my dream cupholder on my dream bag, I want it on the shorter side so it doesn't make the bag wider when turned sideways, and I want it to pivot so the coffee stays upright and doesn't spill when I tilt the bag onto 2 wheels. I don't know if it's possible to design that strong enough not to breaks and slim enough not to make the bag interior smaller, but that's what I'd like.

As is, the cup holder seems more useful for when I sit down at the gate to wait, rather than to use while in motion.