Gabe Aul has hinted that a new Windows 10 Mobile build may be coming to Windows Insiders early next week.
@yosagojimbo Likely early next week.
— Gabriel Aul (@GabeAul) October 24, 2015
The Build that may or may not be Build 10575 will be directly upgradable.
Gabe Aul has confirmed this in his blog post about the Build 10572 too.
Rest assured, if you’re on 10549.4 or an earlier build you’ll be able to upgrade to 10575 (or newer) once it’s out. So if you want to wait for it, we completely understand and it won’t be too long.