What's shown is the ability to change the space between multiple selected layers. I don't see any special "stack" object in the layers panel, or any new properties in the inspector on the right, so we'll see if it's anything more than that.
Considering that the UI that pops up around the layers appears a bit more complex than would be needed for just adding margins, and stacks is one of the top requested features for Figma, I'm gonna guess this is more than just spacing otherwise unrelated layers.
It's Sketch's turn now.
This looks more like Adobe XD's repeat grid. It's a great feature that will save a lot of time during design tweaking but I hope they include the automatic re-ordering and adding of items that Framer X has.
this has a long way to go to compete with framer's Stacks.