Reset Persistent State to Config Settings on Soft Reset
Some machine state is considered persistent, ie does not change across soft reset. This includes things like the joystick type for each port, the ABC/ACB stereo setting for the AY chips and whether each AY is operated in mono or stereo mode. These are made persistent because they are considered properties of a specific "personality" or hardware profile. Eg, if the Next is going to become a 128K Spectrum, these settings would make sure there is only one mono AY chip and that wouldn't change even if the machine is reset.
Although these settings are persistent, they are still modifiable by the user. If a particular game requires Kempston control but the config specifies that the joystick ports are Sinclair1 & Sinclair2, you can still play the game with joystick by changing one of the joystick ports to Kempston through the NMI menu (under NextZXOS), via dot command or by using appropriate REG/OUTs in basic. Likewise some software needs either ABC or ACB stereo to sound right so that can be changed whenever necessary. However, as these settings are persistent, a soft reset to reset the machine does not restore their original settings. The wrong stereo setting can make most games loaded after reset sound wrong. A changed joystick type (which may be done invisibly by a running program) does not go back to what may be expected by the user.
With fixes in recent months, the Next core can tell whether the machine is in configuration or not so it would be possible for the hardware to store configuration settings that could be used to restore settings on soft reset.
If the hardware is made to reset persistent state to config settings, the firmware will also have to be updated so that there are independent configurations for each personality instead of one global configuration for all personalities. This is a good idea in and of itself but without doing this, the current way of setting different hardware after booting a machine would no longer persist across soft resets which is a huge hassle.