Could be. Looks like a duck, quacks like a duck... buuuut...
On one hand, all signs point to Midgardsormr making an appearance in 2.5. On the other hand, he's been the defining feature of Mor Dhona's landscape since 2010. They can't just remove him for anybody that's completed up to a certain point. Forget that people would lose the #1 screenshot destination of FFXIV, but that Sightseeing Log entry would be... problematic, at best, lol. So, how could he return for 2.5 without making that skeleton disappear? In an Echo? As a primal? Summon his essence from the Lifestream? Reborn as Jormungandr? Most of those have a limited shelf-life and if the big reveal was that he was permanently coming back, PR probably would have held that art back a little longer.
Also depends on who you think the dragon in the Heavensward trailer is.
It's been hinted for a long time that Nidhogg would return, and like Midgardsormr he is a king among their kind.