Regardless of the doom and gloom you may have heard, Windows 10 Mobile isn't dead. Its new 'feature2' branch keeps getting updates and fixes. This is 5 build numbers over last fortnight's effort, and features quite a bit new for enterprise and VPN use, plus a truck-load of fixes, as per the quote below. Of personal note is that the fingerprint sensor bug plaguing the Alcatel IDOL 4 Pro and the Elite x3 has now been sorted out.

For 'feature2', think 'RS2+', i.e. 'Redstone 2 Plus'. As before, the Fast Insiders ring for Windows 10 Mobile is becoming less the 'unstable, early access' ring and more the 'more bugs fixed than any other' ring. There's clearly still effort going into keeping the core of Windows 10 Mobile up to date, in parallel with the internals of the Desktop SKU, and fixing reported issues.

From Microsoft:

What's new

Two factor Authentication: We are excited to announce that we’ve introduced a two factor authentication unlock mechanism for Windows 10 Mobile. With two factor unlock, an enterprise can enforce an additional security layer to their sensitive data via an MDM policy. Once two factor unlock is enabled, a phone user will have to enter a numeric pin followed by an enterprise-defined factor to unlock the phone. An example of an enterprise-defined factor is a companion device such as an NFC tag which can be used to unlock a phone using our Companion Device Framework sample app and documentation.

AppLocker Improvements: A number of customers have provided feedback on the warning prompts for apps that are blocked by enterprise policies. We’ve improved the UX and updated the MDM SyncML scripts associated with the policies. Application restrictions can be configured by either the ApplicationManagement CSP or AppLocker CSP. 

VPN Improvements: In the modern corporate workplace, mobility is mainstream and secure access to corporate data via VPN has become the norm. We are bringing a range of improvements and features that enhance the reliability of VPN on Windows 10 Mobile. The key updates to our VPN capability are:

• Lots of reliability improvements for VPN connectivity in Windows 10 Mobile.
• IKEv2 Sleep and Power Enhancements.
  • VPN completes all pending actions before sleep and disconnects.
  • Automatic reconnection on resume.
• Force tunneled improvements for UWP platform.
• Proxy improvements for UWP VPN profile.
• Enabling MMS usage when VPN is connected.

General changes, improvements, and fixes for Mobile

• We fixed a regression that was introduced in build 15245 where the fingerprint reader on the HP Elite X3 did not turn on the screen. You needed to turn on the screen before you could use Windows Hello.
• We fixed some issues where the Maps app navigation would start navigating a route and after performing a reroute, would present a list of possible routes instead of adjusting to the current route.
• We also improved map-matching particularly for routes using ferries.
• We fixed an issue where an app using the routing engine (e.g. Maps) would timeout on providing the route if suspended for more than 30 seconds.
• We fixed an issue where tiles on the Start screen would occasionally be blank.
• We fixed an issue where a VPN profile that was created via the VPN Management API would always be a dial-up profile.
• We fixed an issue with the MDM policy used to control Build Flighting by Mobile Enterprise.
• We fixed a couple of navigation issues when changing from highway to highway (occasionally, signposts were copied from the original highway to the destination highway) and highway to non-highway (erroneous instruction to “enter highway”).
• We fixed a rare issue where the user’s call history was shown as corrupt after an upgrade.

Plenty there to note and take advantage of, then. I should emphasise that, in addition, there are always additional small under-the-hood UAP improvements and fixes which are even too low-level to report in the Microsoft post. 

Anyone with an existing phone that's officially deemed Windows 10 Mobile CU-compatible by Microsoft can join in the fun - in theory. In each case:

1. Head into Settings/Update & Security/Windows Insider Programme.
2. Join the Insiders programme and choose the 'Fast' level in the pick list.
3. Within a few hours your phone should be seeing the build mentioned above and you'll be running the Creators Update and beyond... 

Note that the popular Lumia 930 and 1520 haven't yet been 'provisioned' for this branch of Windows 10 Mobile. I tried - setting the Insider level to 'Fast' doesn't show up any of the recent 152xx builds. Do ping me if this changes, but I'm prepared at this point to say that these 2014/2015 phones may have reached their plateau on the Creators Update Release Preview ring, which will see critical updates through 2017 and then... no more after that.

PS. See also my feature Windows 10 Mobile and the Future: towards Autumn 2018. 

PPS. There's also my feature on upgrade paths for the various classes of existing W10M handsets and the wider grid covering older devices, even though most of these won't be able to take advantage of this (RS2+), even with the Insider programme.