I feel the series is hinting towards it's end with the mention of the 4 red pony glyphs and the events after that happened super fast.
I also think that the series has a good 5-7 maybe 10 years left in it. But it looks like it's forshadowing its closing end.
A few loopholes left are:
Will of D.
World Government and CP0
I can't think of much unless Oda decides to throw in other things arbitrarily like he always does.