For those who asked about temporarily securing a small folding cart to the Mystic Star bag, this is what I used. Purchased on Amazon; under $50 usd, about 3-4 pounds, secured with a few bungees. Once I'm at the gate, I take it off, fold it up and put it in the roller duffel bag.
I also put my 90ish cm Gong carbon mast in the roller duffel bag, not the Mystic bag. I could have squeezed it in the Mystic bag along with other stuff (like the pump) but I just didn't like the board bag being that heavy at all, and it would have been an awkward fit. For all the traveling, keeping the board bag under 25kg was completely worth it for this old guy.
Although the folding roller cart worked adequately as a quick and simple solution for that big trip, I think I could make a custom removable roller setup that would work better ( wider wheel stance, quicker on-and-off, just as light). Maybe a spring project.