Well, he left over behind the scenes politics and disliking RTD's cheesy OTT writing so it's possible he could be back now those elements have gone but... I can't see it. I think he's moved on entirely.
On the contrary, it was because of RTD's writing that Eccleston took the role to begin with. True, behind the scenes politics played a part in why Eccleston left, and it has been rumoured that Eccleston's opinion of RTD has changed since being on the show, never has Eccleston had a problem with the scripts. Indeed, he has singled out Moffat's two-parter as his favourite of the year, but I don't believe he has ever publically spoken negatively about any of the episodes in his run.
Still, I'll be very surprised if Eccleston does show up. I'm pretty sure the Ninth Doctor will be trapped in the vortex.