So I pulled this at a 4v4 tournament yesterday. As my team was comprised of the local Smash 4 TOs, we didn't really want to pull it off because as it's technically a glitch and we should be setting an example. Near the end we came up against another team of some of our friends and (not to brag) we wouldn't have to try too hard to win. So we decided to give it a try to see how it goes.
Would recommend. I got some really early KOs, it was kind of disgusting, haha. Because it's so chaotic, you can move towards someone else's fight and get a sneaky Smash attack and possibly KO. Just be really wary of your teammates... it could end badly if you're just flailing attack around.
In terms of activation, it's worth noting that you need to know where your damage display lies on the bottom of the screen because you'll need to watch for the Art to start flashing. You also need to time it well, factoring that you'll need to call to the Yoshi teammate, make sure you're in their vicinity so they can find you, all so that you can hatch at the right time. It's easier said than done when you want to pull it off, but it's doable.
On a sidenote, I'm not sure if this has been confirmed - this glitch works with Monado Kirby too. However I'm not sure it's worth it quite as much. Kirby can already jump like a pro, the slight speed increase is still really slow. Not sure about the knockback. He does slightly more damage but his range is obviously not as good as Shulk. Even though accessibility is an issue (needs Shulk, Yoshi and Kirby), I still think Shulk makes better use of this.