Should we expect the possibility to flash the rx 580 with an rx 590 for better performance?
No this will definitely not be possible because it's a completely different ASIC GPU chip.
You could do this with certain cards like the VEGA 56 or some older 7950 GPU because they basically had a good ASIC quality but the manufacture just locked the extra cores and sold it for less.
However it needs to be the same chipset for that to work.