Single fiber 10Gb/s X2 or Xenpak transceiver

Hi Guys.

Do you ever see single fiber 10Gb/s X2 or Xenpak transceiver? (I know about
SFP, but never see X2 or Xenpak before)

Haven't seen one. With the huge heat sink and serialization circuitry on
the X2, what advantage would a single strand connector bring? MRV may
have one if anyone does, though.