I mean peering speed between a single pair of ISPs at a single
exchange (or peering) point exceeds that of a single interface.

And, if you need many, say 10, interfaces, l1 have all the
flexibilities Vadim want.

> Layer 1 peering (or pooling, as it's more usually known) is great for
> interconnecting fiber networks, fast provisioning, and all that.

You may say that we are not ready for full fiber networking, yet.

  Any given interface is inherently rate limited.
  When demand exceeds the capacity, something must be
  done. Often this is done w/ "striping" or "muxing"
  where multiple "low-speed" channels are "bonded" into
  a single virtual path. L1 is not that different than
  L2 & L3 in these cases. The specific dynamics are
  unique per layer but the problem remains the same.