Unfortunately missed your AMA, but in case you have time:
You might remember a number of apps which explored this type of pattern on Android and iOS before. It seems pretty clear that it can be used universally.
Some of these same apps moved to something more iOS-standard. Path moved to using a "+" in a tab bar when they replaced their hamburger button. Quora moved theirs to the top-right, or a textbox if you haven't scrolled. Off the top of my head I can't actually think of many other apps that used a button similar to a FAB.
What I wonder is if those changes were made because, despite the pattern itself potentially being superior in terms of ergonomics and discoverability, they're trumped by what users already expect. In the same way that multiple icons are used to convey ideas such as "Share", multiple design patterns across a platform could be confusing. The hamburger menu, for example, I don't think is necessarily a bad pattern, but people who use iOS devices aren't expecting them, because they're not something they typically interact with. I would argue that the best pattern for a particular platform depends on what's been advocated for and most heavily used (tab bars on iOS, for example), because most other patterns require the user to re-learn something just for your app (or in Google's case, suite of apps). I'd be interested in hearing your thoughts about that.
Unfortunately missed your AMA, but in case you have time:
Some of these same apps moved to something more iOS-standard. Path moved to using a "+" in a tab bar when they replaced their hamburger button. Quora moved theirs to the top-right, or a textbox if you haven't scrolled. Off the top of my head I can't actually think of many other apps that used a button similar to a FAB.
What I wonder is if those changes were made because, despite the pattern itself potentially being superior in terms of ergonomics and discoverability, they're trumped by what users already expect. In the same way that multiple icons are used to convey ideas such as "Share", multiple design patterns across a platform could be confusing. The hamburger menu, for example, I don't think is necessarily a bad pattern, but people who use iOS devices aren't expecting them, because they're not something they typically interact with. I would argue that the best pattern for a particular platform depends on what's been advocated for and most heavily used (tab bars on iOS, for example), because most other patterns require the user to re-learn something just for your app (or in Google's case, suite of apps). I'd be interested in hearing your thoughts about that.