I love the feature, but it’s desperately needed on iOS.
I believe Mac Scrivener uses a Mac OS toolkit for this.
Katherine
I don’t really understand what that means on a technical level, but it sounds like you’re saying it’s a Mac only feature because it uses something that’s not available on iOS?
That doesn’t make for much of an argument, since it would be fully possible to create some version of linguistic focus especially for iOS if that’s the case.
I mean, iA Writer has a simpler version of it and has done for ages…
I don’t actually know what the plans are for linguistic focus on iOS. I was just pointing out that Mac Scrivener gets it more or less “for free,” Which doesn’t mean it isn’t possible on iOS, just that there’s more development effort involved.
With all proposed iOS features, though, there’s a tradeoff between features and performance. Even a fully loaded iPad Pro is much less capable than even a low-end Mac.
Katherine
Thanks for the explanation, although this doesn’t strike me as strictly true.
Will keep fingers crossed! 
There is no iOS device with true multitasking, for instance. There is no OS X system without it. Lots of other examples.
Katherine