I think we need to consider the perception of sound quality improvement by Sony will vary a lot.
Users coming from different grades of walkmans:
DMP-Z1 Users
Walkman ZX1 ZX2, ZX300 Users
Walkman WM1Z, WM1A Users
Walkman A45, A55 users
Walkman A100, ZX500 Users
Other DAP users
How much improvement they perceive will depend on which hardware they come from. And also if they had modded their Walkman on the hardware and/or firmware level(non-android models)
Secondly there are group of users who
do not use Sony DSP by setting to Direct Source Mode On, thus do not take advantage as much of the Sony DSP improvements that exist through the years of advancement. They are the group that rely more so on the hardware improvements to the sound, although the firmware software itself still has influence to the sound as experienced by those using
@MrWalkman mods.
What I am saying is the level of improvement of the new Walkman felt by the audiophile community will vary a lot depending on where they come from at the hardware side, along with their own subjective sound preferences, DSP usage, music genre, listening volume levels and what kind of audio gear they have like iems/headphones and the tips/padding and cables used.