Powerline network adapter upstream of GFCI outlet
GFCIs don't care about anything happening on the LINE side.  On the LINE side, GFCI can't influence anything.   

The dominant feature of a GFCI is a current transformer.  Hot and neutral are wrapped around a core, in the same direction so their (opposite flow) currents cancel out the magnetic field.  If not, current is leaking somewhere else. Trip!  Of course this is also a toroid/choke.  Signal can't get through that.  

Since this is a GFCI's core design, there is no such thing as a signal-friendly GFCI.  

Your solution will be fine.  I would push out the junction box to a 2-gang and put the plain receptacle and GFCI right next to each other.  Feed the outlet first, then the GFCI.  Then feed outdoor receptacles from the GFCI's LOAD terminals.  That way the outdoor outlets will be protected, but the GFCI will be indoors where it will last.  GFCI's do very badly outside.