Heh, for some reason, you just reminded me that Serra has a pretty bad Vanguard card...
Is Serra being back as a planeswalker new to this exciting set, or something I missed from the past year or so?
Not sure exactly what you're asking, so I'll try to explain...
-This will be the first planeswalker card with Serra as its planeswalker subtype.
-There has never been another Serra planeswalker card (unless The Wanderer is secretly a resurrected Serra somehow, but that sounds way more awesome than anything WotC would do with the story).
-We have no indication that Serra is
back in the story, if that's what you mean. But that situation is a
total mess, which I'll try to explain below...
-This new set isn't meant to advance the normal story being told in the Standard expansions and Serra's presence in this set might have no lore significance at all. WotC have an established track record of using non-Standard sets to print cards that they can't thematically work into the main story. For instance (perhaps feeling like they needed to make a particularly silly blunder) they chickened out of reprinting the popular card Inquisition of Kozilek when the character Kozilek came back into the story for
Oath of the Gatewatch. Then they killed Kozilek off, so they lost their chance to reprint it at all. To correct this mistake, they reprinted the card in
Conspiracy: Take the Crown and in
Modern Masters 2017 because those non-Standard sets didn't need to follow the regular storyline.
-Basically, this is like when they printed a Freyalise planeswalker card in
Commander 2014. Freyalise as a story character had already been killed off, but they didn't need to do story stuff to use the character on a card in that product.
So as far as we know, Serra is dead in the Magic story, but this character has had perhaps the most confused, most retconned story out of anyone else in the major lore. Writers for official Magic materials have contradicted each other on where Serra comes from, how she got her name, what happened to her on Ulgrotha, the circumstances of her death, the ultimate fate of the plane she created, and what lingering influence she may or may not still have on Dominaria. Part of the problem is that some of the details about her life come from the
Scourge novel and the people with creative control (and possibly everyone else too) just dislike everything about that novel.
It seems pretty consistently that Serra is depicted as having died on Dominaria, though.