One major figure on the MTGSalvation forums is heroicraptor, a rules advisor who's been known to get rumor tips in the past. Today, raptor posted a Spanish-language promo card of a nasty rare burn instant that purports to be the Theros Buy-a-Box promo:
Nefarious Burn? 1RRR
Nefarious Burn? deals 5 damage to target creature or planeswalker. If it's your turn, scry 2.
Between this and Hero's Downfall in Theros, it looks like R&D is really pushing for good combination creature/planeswalker removal. Of course, direct damage that specifically hit planeswalkers was unheard of until Magmaquake a couple of core sets ago, because of the player redirection rule; but now it may well be kosher to use more often. After all these years R&D may be comfortable broaching the subject of planeswalkers in the text of non-planeswalker cards - who knew?
Four mana for instant speed removal of two card types is always a good deal - and Nefarious Burn has that bonus for using it at sorcery speed as well, which puts it over the top into a really strong card. Slower, more controllish red archetypes would relish the ability to blow up a threat and stack draws into more damage spells at the same time. Could this be the sign of red getting its share of the monocolor devotion goodness in Born of the Gods, with possibly three partly-red gods ready to be printed?
The pseudo-Sulfurous Blast clause is certainly out of the ordinary, and could mean a "Nefarious" cycle much like the one from Time Spiral.