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.
Yep, RX590 is an entirely different architecture. You can't flash the BIOS and wish your RX580 will become a 590.
But it wouldn't probably works like it should If you would try that let me know result 