Hello Pavel, are you talking about Wiznet? Evaluated that way, too slow in my apps but actually using two chip raise too much the uncertainity.
Wiznet has some ARM based chip can solve all but again a lot of cheap board not so many chip on standard market.
This remember Elton John album "Goodbye Yellow brick road"
too old to rock and roll
too joung to die
Actually good idea but caveat is in your word "any available STM32". :anxious_face_with_sweat: Non STM part suffer same or worst rule, PHY or complete SPI MAC leave procurement at same confidence.
