@RickM.:
My guess is wind logia, its what makes more sense to me, but that wouldn't explain why he created that lightning back at Logue Town, unless he could manipulate the weather with his winds so he could created lightnings, like Nami does.
Pretty much this. There's just too many leads and hints on it being Wind but the biggest to me would be what Wind represents in the Japanese philosophy. I already linked this in one of my recent posts but here it is again. For instance, Fire representing "represents the energetic, forceful, moving things in the world" and being associated to "security, motivation, desire, intention, and an outgoing spirit" both fits Ace's character and what he represented into the story, also what his death symbolized. The same way as how Sabo is being represented into the second half of the story. The void is Blackbeard, not that it's not obvious. Speaking of Sabo, before he came along, it always been the D's who has had 2 of those elements (3, if Dragon does have Wind).
Now the lightning/weather itself I don't think is a Devil Fruit. I posted this in my own thread (under "Dragon") but it has connections to Ki. It's just speculation at this point but the weather changing has also been portrayed in Chapter 0 with Roger's battle with Shiki's fleet. There are two possibilities: it could be literally portrayed easily as that is "dumb luck" or to quote Smoker in Logue Town "It is like heaven itself is keeping that man alive". This is where it gets tricky, by that quote it could still be dumb luck, however weather is "Tenki" in Japanese (Ki is involved), Ten Ki is literally Heavenly Ki. By "Heaven" it could literally be the dumb luck or Dragon/Roger's doing - like what do you know? Both being D's which are portrayed to be the natural enemies of the "Gods" in the series. "Gods" that can bleed ('Devas') and are assumed at this point to have been responsible for the destruction of an Ancient Kingdom that is most likely related to the D's - basically it seems like an old story of usurping. The D's and Celestial Dragons though, as in the Asura and Deva, if in the case of it being a usurping story, it could honestly be interchangeable as who fits whose role. Welp.. something like that anyways. That's all I got.