Fair catch is the best analogy, as posted above. The play is dead at the initiation of the slide, just like the ball is dead after a fair catch. Even if the receiver drops a fair catch and recovers the muffed punt, he still can’t advance because he has “given up” the right to advance. Starting a slide is the same thing. The QB has “given up” the right to advance. I was honestly surprised that they weren’t already administering it that way to begin with.
Now, with that being said, it was a heck of an athletic play, and as an objective third party, it was funny to watch the defenders freeze just long enough. But I’m glad they will now call it dead at the start of the slide.
But the next interpretation issue will come in about a year when a QB starts a slide and fumbles before he hits the ground. And the internet will blow up. 😂