Accepted gts trade, didn't show up on there, wifi it says it.
I have yet to develop control test, since my trade got through GTS.
I'm gonna try Wifi Trade now.
However there is hope for my method, as my Shiny Flabebe appeared on GTS:
EDIT 1:
I've hit a snag.
My pokemon could still be traded across Wifi, before any prerequisite trades
I'm now attempting to Wondertrade my powersaved shiny (another new one),
To see if the message appears.
EDIT 2:
On my first trade, the shiny got across the wondertrade, with no prompt.
So Far I'm having no issues with shinies from powersaves being traded off.
EDIT 3:
Without any initial trades,
My shiny can be seen from GTS.
I have no idea what issues you encountered with Nyancat,
But Mine are all showing.
Summary (virgin trades for the Powersaved Shiny Pokemon):
Wifi:
PASS
GTS (deposit):
PASS
GTS (seek):
PASS
Wonder Trade:
PASS
If TL;DR:
I did not encounter any issues regarding trading and powersaved shiny.