A friend of mine said the "father and son" thing could refer to Natsu and igneel,not just Gray and Silver.So,Mashima could really be trolling us.
But...the only thing that would make Igneel appear by his own volition would probably be E.N.D's awakening.But...well,the book got petrified along with Marde.That is not definitive since the king said he is going to leave Marde's downfall to Fairy tail.It seems to soon for E.N.D to hit the stage.
Well,up till now Mashima didn't troll us with the chapter names.Well,he did somewhat with "the king of hades",since it seemed E.N.D would be awakened.But the others were played straight.
The name of the next arc "Father and son" resumes what will happen in it.However..."Song of the celestial dragon" referred to an event that happened in the last two chapters of the arc 2,Wendy activating dragon force and wrecking face.Since each arc has 8 chapters,we have an 1/8 of a chance to see in the next chapter whatever the title refers to SIlver and Gray or not.
Also,Everyone was thinking that lightning flame dragon mode was a one time use for the batle agains master Hades.Well,Natsu learned how to use it later,even though it lacked the same destructive power.Maybe Lucy can still use Aquarius's power?But yeah...she did lose the tattoo.Oh well,we need patience.