Predicting Marvel villains and direction of their future universe is nearly impossible. Kevin Feige and the folks at Marvel Studios have had a decent lock-down concerning their future plans, for the most part. While we've had both Feige and Gunn shoot-down a bunch of rumors lately, mainly talk of a Ms Marvel (even though she's expected to show-up in Age of Ultron) film and the Planet Hulk storyline being explored. I think we're all overlooking other things that could be coming out of the cosmic-side of the MCU in the near future.
James Gunn revealed to ThePlaylist that Marvel has a very limited access to villainous alien races from the comics, pointing out they don't own the Badoon. I assume Fox has those rights from their original deal for Fantastic Four/Silver Surfer. Strangely enough, we saw almost zero aliens in that original franchise. Even though Fox has access to characters like The Silver Surfer, Super-Skrull, The Badoon, Blastaar, Galactus and possibly even Kang The Conquer (someone needs to ask Feige about that one).
"The whole thing is, there's Sakaraan in the movie. And the reason there's Sakaraan in the movie is because there aren't that many alien races in the Marvel Universe, and of those prominent alien races, such as the Kree and the Skrull," Gunn added, somewhat tantalizingly, "I have some very specific ideas for where those races go."
Gunn did however mention that he and Marvel have plans for the Kree and Skrulls. The bitter alien enemies, whose war has spanned across the universe and even clashed on Earth as well. Interesting enough, Thanos has connections to both The Kree and The Skrulls, the Skrulls being one his pawns similar to the Chitauri. Yet, considering their advanced technology and shape-shifting abilities, they would make a stronger threat to the Earth (ala Secret Invasion). I could also see them become the antagonists for the Black Panther movie as well. Whedon has said as much, while opting to use the Chitauri instead of the Skrulls for Loki's army. Marvel seemingly has big plans for the two alien races. Perhaps, those plans will be revealed this weekend.
Ronan The Accuser the main baddies in Guardians is indeed a high-ranking Kree, who just happens to work for Thanos. So the Kree have already been established in the MCU, and talk of Ms Marvel could mean their involvement on Earth soon. Ronan might also have ties to another villainous group under the thumb of Thanos. Considering their connections to Thanos and doing his dirty-work, I'm assuming both Ronan and Nebula are Thanos' generals in his group The Black Order. I'm actually curious to learn why the Kree (or just Ronan) is backing-up Thanos. Perhaps, Thanos is actually in-control of the Kree Empire at the moment. It will be even more interesting to find out how The Inhumans fit-into all of this as well. Since that film has been compared to Game of Thrones in space.
I wouldn't be too shocked if we end-up seeing the rest of Black Order (Proxima Midnight, Corvus Glaive, Supergiant, Black Dwarf, Ebony Maw) in the sequel (if not in other Marvel films), searching the rest of the universe for Infinity Stones/Gems. Clashing with the Guardians and other cosmic heroes along the way, leading-up to the eventual Avengers 3 confutation. There have been teases that the Guardians could crossover into an Avengers installment, which makes sense since Thanos would be everyone's problem by that point.
We've been hearing for a while now that Thanos (played by Josh Brolin) will be the big bad of the Marvel universe for years to come. Being a kind of puppet master, pulling the strings of other powerful Marvel villains. Having his Black Order on the hunt for the infinity stones sounds about right. It's also in his wheelhouse to spark a huge conflict on Earth like either an invasion or all out war by the Kree and Skrull. Leading to all sorts of possibilities such as Secret Invasion or even Civil War.