Currently, of the four BIG pairings (NaLu, Gruvia, Jerza, and Gajevy), Gajevy is established, Jerza is built and just needs the final confirmation, and Gruvia is just a step away from establishment. Only NaLu remains underdeveloped.
Throughout 100 Year Quest, there were progressive moments of teasing: Lucy calming Natsu down from his rampage fighting Mercuphobia, Natsu driving off guys hitting on Lucy, Lucy being teased about Touka being a "love rival", Lucy embracing Natsu after he defeats Aldoron (as seenon the cover of Chapter 63) and most recently, Natsu feeling good in Lucy's bosom (and that's not counting their encounters with their doubles). The question basically amounts to how the two are going to develop into something more substantial. I'm skeptical that we'll seeing much substance in this arc, but I'm still holding out hope (nure-onna Lucy is a prime opportunity, but so far, it has been taken). One possibility is Ignia kidnaps Lucy, knowing it'll provoke Natsu.
Honestly, if after all this teasing, NaLu remains the only pairing that doesn't get confirmation, that would be a slap in the face to the readers.