Android, in each version, strives to be more secure, and it passes through difficult tasks having to do with the root (modules, ROMs, recovery…), and it seems that in 7.0 Android Nougat a step has been made later with its reinforced verified boot which, moreover, will have the ability to correct certain errors.
This system would do that If the ignition system is corrupt, the terminal would not begin or allow it the user, would do it in a limited way. This strict check could do those not malicious corruption began to have more impact on the system, when before they were not detectable.
The verification system could even correcting certain types of errors during startup, Although by now limited to a few to avoid overloading the storage already on its limited our smartphones. Even though this start verification system improves safety, it also reduces their reliability by increasing the impact of the corruption of the disk that can occur in the device due to hardware or software issues.
The correction system, that Yes, promises make devices with Android Nougat more safe and reliable at the time not overloading both storage (it would only be a 0.8%). In short, it is possible that it is much more difficult to install ROMs custom in the new version of Android due to this even more reinforced boot method.