The "Coming Soon" toggle appeared in my Outlook (Insider) today independent of a new build. However, enabling it and restarting Outlook doesn't change anything that I've noticed, so maybe actual changes will require a new build. Update: Enabling it on a different system (same Insider build) DID enable the changes though, so maybe it's just a slow/targeted rollout, even for those who opt in.
Alexis Menard, that reminds me of many years ago when we could also simply delete an email right from the toast notification (there was an "X" on one side of it). I assume, like the actions you mention, this capability was lost when Outlook opted to use Win10's notification system. I'm amazed that these features haven't been restored yet, but I have a feeling that it's yet another limitation of the system (i.e. the OS, not Outlook).