I think that's true; it would be very surprising if at some stage in the future CX were not a customer for the 777-9X. That pretty much kills the 747-8.
The problem for the 747-8 is that it's at the end of the 747 line, whereas the A380-800 is the first in that family; sure CX would prefer the -900, but given the right price and commitment of the -900 at a certain time in the future, I think CX can be tempted to go for the -800.
CX has said that a decision can be expected around the middle of this year and now we're in May; perhaps something to be announced at the Paris Air Show?