Since Microsoft began working on the Fall Creators Update for Windows 10, its phone platform, Windows 10 Mobile, was moved to an entirely different development branch - feature2, rather than Redstone 3. Speculation over these split branches grew over time - some assumed they would merge back together after a few builds and that Microsoft would continue adding features to Windows 10 Mobile; others claimed it would be staying on feature2, effectively creating the last major update for Windows 10 Mobile as we currently know it.
As noticed by Neowin, in the Windows Insider team's monthly webcast, the team were asked whether Windows 10 Mobile would be leaving the feature2 branch - the answer: no.
The feature2 branch will be the branch where the next update for Windows 10 Mobile is coming from, and with the lack of new features being implemented since being on this branch, it is safe to assume that Microsoft considers the current implementation of Windows 10 Mobile as feature complete. The next interation of their phone plans appears to lie with adaptable CShell that we've seen recently, however, this is only expected to arrive on new hardware - if so, current devices will become obsolete.
All in all, don't expect to see any new features on Windows 10 Mobile.