I hoped that with the fiber, which is naturally full-duplex medium, symmetrical speed would be obvious choice. But with advent of GPON, which is essentially half-dupex shared fiber medium, asymmetrical speeds make sense again.

Here, a provider i use offers variable tarrifs, that allow adjusting download/upload ratio dynamically in web interface (e.g. tarif '250' could be switched between 250/80 Mbps, 150/150 Mbps, or 80/250 Mbps).