If there is no GDC and given how well GW ran in the Irish Gold Cup (despite pulling far too hard), I would say they might think there is unfinished business at Leopardstown too – he has also grown up plenty since those poor runs at the track.
I do agree that Kitzbuhel looks tailor made for the King George (after his Kauto Star Novices Chase win) and the fact that he simply outstayed Final Demand in the Brown Advisory (no real excuses to me) makes me think he could also be a live contender for the Gold Cup itself down the line.
I do wonder whether Mullins would consider sending one of them over for races lke the Charlie Hall and/or the Betfair Chase at Haydock (where he will almost certainly get the soft ground he is looking for 
)
The John Durkan could be a real interesting starting point next season as you could see all of the above (and likely some others) turning up for it given Mullins does tend to go mob handed in the race (he had 6 of the 10 runners this season).