2015's plans to use Galactus and Annihilus as villains are excellent for Marvel Studios and the Marvel Cinematic Universe going forward, especially regarding the company's so-called "first family." Both of these comic book antagonists have been major players for years. Thanks to the canceled plans involving the antagonists, their eventual MCU debut can be even better.
Galactus, originally Galan of Taa, was first seen in Marvel comic books in 1965's Fantastic Four #48 in a landmark issue that also saw the return of the Watcher and the debut of the Silver Surfer. The terrifying Galactus is known as the "devourer of worlds," and he lives up to the name. Annihilus, the insectoid ruler of the Negative Zone, would appear just a few years later in 1968's Fantastic Four Annual #6. According to screenwriter Jeremy Slater, these two were meant to be the main villains in early drafts of 2015's Fantastic Four. The production of that film was a complete disaster, and both were eventually taken out of the movie altogether.
Had the duo appeared in 2015's Fantastic Four as was originally planned, it's likely Marvel Studios wouldn't want to either of them going forward. The film giant is keenly aware that MCU fans are salivating for a new Fantastic Four, judging by Avengers: Endgame, they're lucky to have both Galactus and Annihilus ready for future movies. Given they could be two of the MCU's biggest future villains, both in Fantastic Four movies and beyond, it's nice that there's something of a clean slate for Hollywood's biggest film franchise.
While it seems like Marvel Studios is setting up Kang the Conquerer as the next "big bad" of the MCU, throwing in the likes of Galactus and Annihlius along with him could be great. If the franchise is truly going to get weird with the Multiverse, they might as well go all-in and bring the Negative Zone to the big screen as Slater initially intended. The wild and dangerous Quantum Realm has already been seen multiple times, priming moviegoing audiences to be prepared for weirdness.
If Marvel decides Annihilus is too out there for the first Fantastic Four outing, bringing early Galactus stories like "The Coming of Galactus" or "Behold... Galactus!" to the MCU would be a safer bet. Doing so would also allow Marvel Studios to bring the Silver Surfer to the masses again. 2007's Fantastic Four: Rise of the Silver Surfer certainly did no justice to either the Surfer or Galactus. Marvel Studios head Kevin Feige was an executive producer on that project, and he'd probably like to have another shot at adapting these two Marvel titans.
Marvel is going full steam ahead with their Fantastic Four movie, and longtime readers of the group are hoping to get a faithful representation of the heroes. There is even an opportunity to bring in the Richards children this time around. Every attempt at bringing the Fantastic Four to theaters has ended poorly thus far, and the MCU needs to get the Richards family right. Part of the winning equation should include having a non-Doctor Doom villain at the forefront, and either Galactus or Annihilus would be a great choice.