On this one, I agree with you.

The whole gesture interface they have proposed seems broken, not only the 3s multi-tasking view.

Too bad they don't seem to have read what Jaakko Roppola explained a long time ago (and that even Jolla broke with Sailfish 2, in place of fixing what was missing in Sailfish 1...), like this article:
https://jaakkoroppola.blogspot.fr/20...-gestures.html

First, the interface is not symmetric, so right handed and left handed person would not have the same actions easily accessible.

Then, as I see it, the most important function in gestures would be the return to home screen or multitasking view depending on the OS design principles (would be multitasking on N9, home screen on Android or Symbian for widget access, kind of a combo on Sailfish).
As the most fundamental action, this should have been an edge swipe. But no, the upper right edge swipe is "most frequently settings". And they have hidden the multitasking action behind a 3 seconds delay on the bottom and the homescreen action on the lower swipe.

The secondary most important action would be in my mind the events view. Any well designed OS uses this event view to provide all kind of informations about communications, calendar, etc. and is used to see the details and eventually directly reaching the dedicated application to go further. That is a lot more powerful then launching individual apps and navigating through them to find the info. Following Jaakko principles, this would be on the lower swipe. Here, they put it on the worst place possible for a right handed person: top left edge swipe...

For the rest of the actions, I can say the quick launcher idea can be interesting, but the home-screen role should not be that different to need a different concept.

The multi-tasking view as a carousel they show has the advantage to be easily clickable from about any point on the screen, whereas tiles (like in the sailfish 3x3 grid) can be hard to reach if too small and to far from the thumb rest position (like the top left on sailfish for right handed persons when there are 3 columns). The drawback is that it is harder to quickly spot a specific application if you have a bunch running (as would be expected from a real multitasking phone).

And last, I don't know in all of that how you can start a new application. There is no app launcher ? Would this be on the homescreen ? Jolla made the mistake to put it on the bottom swipe in place of the event view (that is now hidden behind the homescreen) as the second most important action, where it is secondary you mainly are using apps already launched or opening them in reaction to notifications. But it should at least be somewhere...

So far I liked what they where proposing, but this UI post left me wondering about what this will look like in terms of usability out of the box.