Rough estimate is the Outlook app has over 70k lines of Swift, which is just over 50% of our codebase (the rest is Objective-C). That doesn't include external libraries.
One of our devs starting adding Swift code to the project about a year and a half ago. After that proved successful, the rest of the dev team then started getting up to speed. For the last 8 months, all development has been done in Swift.
We don't arbitrarily rewrite existing source, but if we're making changes to an existing Objective-C file, we evaluate if it would be worthwhile to rewrite in Swift. Often the answer is yes.
From our perspective, Swift is absolutely ready for primetime. For a large codebase like ours, it takes some time before you see direct benefits, but if you keep with it, I'm sure you won't regret it.
I should mention the downsides: the migration to Swift 2 took time, but it wasn't awful. I'm sure we'll have similar issues moving to Swift 3. Also our compilation times are quite a bit slower than with purely Objective-C.
I don't know what the solution is here, but I'm worried that if we don't implement this solution, the web will fall even faster out of favor to native apps.
I'm talking about mobile.
Right now running flash or silverlight on your desktop is no big deal. This "solution" is unnecessary. But on mobile we have a real problem: the only way for anyone to deliver encrypted media is via a native app, which is exactly what everyone is doing. That comes at the expense of the web. So now we have an entire generation of users growing up on apps (netflix, hulu, spotify) because those content licensing deals require DRM.
The desktop is fading. If we want the web to stay relevant as everything moves to closed ecosystems, this may be a necessary evil, because the web+EME is infinitely more open than the an iPhone/Android app.
I'm sure they want you to use the iOS Gmail app. While it doesn't support true "Push" email, it does receive push notifications which is a pretty good approximation.
One of our devs starting adding Swift code to the project about a year and a half ago. After that proved successful, the rest of the dev team then started getting up to speed. For the last 8 months, all development has been done in Swift.
We don't arbitrarily rewrite existing source, but if we're making changes to an existing Objective-C file, we evaluate if it would be worthwhile to rewrite in Swift. Often the answer is yes.
From our perspective, Swift is absolutely ready for primetime. For a large codebase like ours, it takes some time before you see direct benefits, but if you keep with it, I'm sure you won't regret it.
I should mention the downsides: the migration to Swift 2 took time, but it wasn't awful. I'm sure we'll have similar issues moving to Swift 3. Also our compilation times are quite a bit slower than with purely Objective-C.