The story so far then.... Windows 10 Mobile wasn't, at one stage, going to get 'Redstone 3', a.k.a. 'Windows 10 branch 1709' (i.e. 2017, month 9) at all - after all, Microsoft had stopped making Lumias a year before. However, there were still enough people and companies using the phones - plus the ongoing sales of the Alcatel IDOL 4 Pro, HP Elite X3 and then finally the Wileyfox Pro - that support needed to carry on for significantly longer than 'Windows 10 branch 1703' would allow.
Which is where the faux-Redstone 3 came in, a branch wholly for Windows 10 Mobile, 'feature2_rs3', which is part Redstone 2, part Redstone 3, in terms of how it's bolted together. But there's enough that's Redstone 3 for the official branch number to be '1709', along with the rest of the Windows world. End users know this as the 'Fall Creators Update' - as terrible a name as the 'Spring Creators Update' and it's no surprise that Microsoft has now stopped this trend and started just quoting the date of release!
In case you need a ready reference for all the various equivalencies:
|Branch||Build nos||Codename||End user name|
|1703||15063.nnn||Redstone 2||"Creators Update"|
|1709||15254.nnn||Redstone 3||"Fall Creators Update"|
|1803||17134.nnn||Redstone 4||"April 2018 Update"|
However, Microsoft's gameplan has shifted in terms of adding inking, Mixed Reality, 3D, Timeline, Sets, etc. to the main Windows 10 builds for Desktop and also for Hololens and even XBox (where appropriate), necessitating new APIs, Application Program Interfaces, essentially letting third party applications access some of the new features, especially in newer hardware. Note that doing all this doesn't mean that Microsoft can't come back in Mobile, since telephony is still baked into Windows 10 and a future Surface Mobile (and clones?) would use all the new stuff in hopefully new and interesting form factors.
But judging from the article linked above, just one example from recent fare, more and more 'advanced' functionality is being linked to branch 1803, i.e. Redstone 4, the 'April 2018 Update', and beyond. Although most third party developers are still only requiring branch 1703 to run their UWP applications, there are some now quoting 1709 (fine for most people reading this, I suspect, on relatively recent devices), and some also now compiling their apps against branch 1803 APIs.
Which is what we're starting to see even with Microsoft's own core applications, with this highlighting of Edge's push notification capabilities just the tip of what will be revealed to be a larger and larger iceberg.
This week saw Twitter, the leader in mainstream PWAs by quite some margin, updating its PWA in the Microsoft Store. And on the Windows 10 Desktop it's essentially a full replacement for a native Windows application, complete with notifications, provided the user is bang up to date with Windows 10 'April 2018 Update'. However, under Windows 10 Mobile it's crippled by the Edge browser version being too old to have working support for service workers, background updates and push notifications.
Just slightly too old. The various hooks are there in the UI to enable all this functionality, you can see for yourself in Edge by typing "" into the URL bar. Feel free to turn on '' and '', but they won't work properly - Microsoft simply never finished this code in Edge on the 1709 branch.
Which is why a new branch of Windows 10 is needed if PWAs are to be taken seriously on Windows 10 Mobile for the rest of 2018 and all of 2019 (to the stated end of updates for branch 1709). No, Microsoft doesn't have to put massive effort into back-porting the vast amount of new code from the Desktop builds. But a 'feature2_rs4' branch with the '1803' kernel and EdgeHTML engine and other relevant modules would be relatively trivial to implement.
It may be, of course, politically inconvenient for Microsoft to throw Windows 10 Mobile another lifeline - extending the support period again, this time to mid 2010, would mean resources tied up in the future building updates for an OS 'from its past' even while Surface Mobile (etc.) might have been on sale for well over a year by then.
No doubt there's a wall chart at Redmond planning all this out and I'd love to get a peek at this.
In the meantime, 'feature2_rs4' and fully functioning PWAs, anyone?
PS. If you're looking into the April 2018 Update on your Desktop, then I can recommend WC's coverage, indexed here.