First any storytime, but Son of He-Man! Keep this bad idea exclusive of the Classics mini comics, but OUT of the DC MOTU Canon. The main MOTU cast is still young in the DC continuity, and with a lot of stories to tell about them, and shape them again as characters. He-Man and Teela have not been even been established as a couple in the comic, apart from a kiss as kids, for make such a jump (let's have their relationship better fleshed out, and then will see about children). Besides the MOTU franchise is relatively small now for trying to dilute what's left of it with legacy stories, and this could drive the remaining readership away.
If the comic continue beyond the Eternity War, there are a lot of possibilities for new stories:
- A devastated post-Eternity/Apocalyptic War Eternia would be similar to this of the first barbarian, Sword and Sorcery mini comics. With the void of power created after the War, many new Warlords or Wizards can see this as opportunity to take over. Various independent villains can appear from the previous MOTU canons, like Count Marzo, Prahvus, Shokoti, Lodar etc or completely new ones never seen before. I can see Skeletor trying to recruite a new bunch of Evil Warriors apart from the 5 that appeared in the comic, like Jitsu, Spikor, Webstor, Two Bad etc. And He-Man trying to fight threats through this new kind of war, while struggling as young King to bring piece in a devastated world, finding new allies between old foes (see Sy-Klone).
- There is also King Hsss and the open question that is the Snake Men! What are they going to do after the Eternity War? Are going to remain allies with the rest of the Eternians or will go back to their King and turn against them (i.e. Serpent Wars)?
- There is Marlena that she is still stuck on DC Earth, and the possibility for a new crossover with the DC heroes, this time with She-Ra being among the crew as she will want to meet her real mother.
- There is Orko that he is stuck on a world called Netherworlds as Skeletor called it. He-Man has promised that he would try to find a way to bring him back.
If instead they want to get more profound to the MOTU mythos they could explore Preternia, telling a more deatailed story about King Grayskull, Veena, He-Ro etc. Or they could make a story about the 7 years old war that raged on Eternia between He-Man and Skeletor, before the DC MOTU storyline begun.
As for Etheria i can see makėng a new spin-off mini series that accompany the MOTU comic, with Hordak surviving from his last battle with Skelly, but stripped of his mystical powers since the Souls and Grayskull are not his anymore, being reanimated as a cyborg technological villain, and return on Etheria to regroup, since i can't see him to invade Eternia for the near future after such defeat. Meanwhile She-Ra stuck on Etheria as well, join the Rebels, and the story continues.
Of course all of this is speculation, because we have no idea or information that the story will go further from the Eternity War. The most important thing for now is to know that the DC comic continue. Then the possibilities for new stories for a franchise like MOTU are limitless. Creative imagination needs it and good will.
Ah, and something else of crucial importance: If the comics continue KEEP THE SAME CREATIVE TEAM! Meaning Dan Abnett, Rob David, Pop Mhan and Mark Roberts! Team that is successful, doesn't change! Would be cool also to have Stjepan Sejic and Dave Wilkins return to do some covers. Or some of Axel Gimenez's magic parhaps.