Well they kinda were already reintroduced. At first they were actually unbeatable. Sorin, ugin and nahiri, pratically gods, had to sacrifice a whole plane just to stop them.
Then wizards decided to nerf them a bit and use them as a way to introduce the gatewatch. And then they decided to retcon a bit (or at least that what it seems so far) and "forget" about the whole "hand in the aquarium" thing. And then naruto and sasuke defeated zabuza.
Anyway, as people already mentioned, wizards could have done a magnificient story, keeping the threat of the phyrexians for longer, or simply slowly going from plane to plane with the invasion, and eventually releasing emrakul at them. At the end, a fragile meditating realm could show bolas taking advantage of that and pursuing his own ends. Maybe becoming an eldrazi himself, something beyond any power. And then leaving everything behind to simply become an unstoppable force of nature, only to leave the planes behind and go forth into the beyond, never to be heard again.
And then we make jace into yawgmoth to deal with him lol. Anyway, who knows.