Sooner or later, Galactus will make it to the MCU. When he does, he will undoubtedly be preceded by his heralds, and that's why you should be collecting their first appearances now.
Absolutely nothing has been said specifically about Galactus in the MCU. There's a plethora of speculation and rumors about the Devourer of Worlds being a major villain going forward, but Kevin Feige and company have said nothing on the subject. For that matter, Feige has revealed little about any plans for the newly-acquired Fox properties.
Still, there's no way Marvel won't put Galactus to use. He's one of the most awe-inspiring villains the Marvel Universe has to offer, and he has legions of fans. Those facts are partly the reason his first appearances in Fantastic Four #48 and #49 are holy grails with the price tags to prove it. That's why you should be looking at the debuts of the Heralds of Galactus since they are essentially two parts of a whole.
It would be easy for Marvel to have a reverse-Avengers introduction for Galactus. One by one, the heralds are brought into the MCU and slowly pieced together until they finally trumpet the coming of the World Eater. The fact that Marvel is focusing it's efforts on the cosmic side of things lends to reason that this could become more than speculation on my part.
Over the decades, Galactus has empowered many beings with the power cosmic. Some lasted for years, others were more short term. Below you'll find seven of his most prominent heralds (not named Silver Surfer) and their first appearances.
AIR-WALKER
FANTASTIC FOUR #120 and THE MIGHTY THOR #305
Chronologically by publication date, Air-Walker is the second-oldest herald after Silver Surfer. He initially debuted as an android in FF #120, but in the pages of Thor #305, readers saw him in his true form.
FIRELORD
One of the better heralds, Firelord has endured as an important part of Galactus history. He made his first appearance in Thor #225, and he has gone on to face many of Marvel upper echelon of heroes.
TERRAX
My personal favorite herald, I can't picture Galactus being introduced without Terrax connected in some form or fashion. Like Air-Walker, he premiered in the pages of Fantastic Four.
MORG
Morg the Executioner took over as herald following Nova's expulsion for sparing too many planets. It makes sense that he debuted to battle the Surfer.
RED SHIFT
Using two magic swords that can cut portals through space, Red Shift made his mark in the first issue of Galactus' self-titled series.
STARDUST
STORMBREAKER: THE SAGA OF BETA RAY BILL #1
With everything Beta Ray Bill heating up, this could eventually add value to the issue. Considering Stardust's connection to Bill and all the rumors of his appearing in the next Guardians of the Galaxy film, it would stand to reason that Stardust could have a featured role as Bill's antagonist.
THE FALLEN ONE
As far as comic history, the Fallen One is said to be Galactus' first herald. Not much is known about him other than he became so powerful that Galactus imprisoned him, though the Fallen One escaped. Although he was mentioned in previous issues, the Fallen One didn't make his actual debut until Thanos #11 in 2004.
