Marvel's Agents of SHIELD has begun to set up the return of Gabriel Luna's Ghost Rider. Marvel Television has confirmed that seasons 6 and 7 of Agents of SHIELD will be the last. They're aiming to end the show on their own terms, and as part of that they want to tie up any major loose ends.
One such loose end is Gabriel Luna's Ghost Rider. Introduced in Agents of SHIELD season 4, Ghost Rider was a phenomenally popular character. Marvel recently revealed that Luna would soon be starring in his own Ghost Rider series, which will air on Hulu in 2020. This is expected to be independent from Agents of SHIELD, and as such it would make sense for Marvel to wrap up Ghost Rider's relationship to the clandestine superhero spy team.
Marvel seems to have begun setting up Ghost Rider's return in the latest episode of Agents of SHIELD, "Leap." They've finally revealed the truth about Izel and Sarge, two powerful but mysterious beings who have literally been destroying entire planets. It seems they're from another realm, one inhabited by non-corporeal beings, and Izel seeks to launch a full-scale invasion of our plane of reality so her people can claim physical hosts. At the end of the episode, Fitz explicitly compares Sarge and Izel to Ghost Rider, and contemplated just how powerful they could be. The Agents of SHIELD season 6 trailer released at SDCC 2019 confirmed that Fitz is wise to worry; it showed Sarge wielding colossal power.
Essentially, the SHIELD team is dealing with the MCU equivalent of demons; non-corporeal beings from another plane of existence who crave physical form, and seek to take possession of hosts. As Fitz notes, they're the same kind of creature as the Spirit of Vengeance that drives the Ghost Rider - but there are a couple of subtle differences. The MCU's Ghost Rider seems to partner with its host rather than outright possess them, and allows the host a greater degree of autonomy. What's more, it seemed to be even more powerful than Sarge and Izel; Ghost Rider could open portals through the Multiverse at will. If Izel and her kind could do the same, they wouldn't need the Monolith energy.
Agents of SHIELD's season 4 finale, "World's End," saw Ghost Rider reveal that Earth "is just one territory in a war that's been going on forever." Some of the creatures of the Multiverse are good, while others are malevolent; for all his fiery visage, Ghost Rider fights on the side of the angels. It's safe to assume Izel and her kind are an opposing faction. And in Agents of SHIELD season 4, Ghost Rider was drawn to this kind of crisis, able to sense the interdimensional disruption. With the scale of Izel's threat increasing, it wouldn't be a surprise to see Ghost Rider arrive on the scene to give SHIELD some much-needed backup. The synopsis for the Agents of SHIELD season 6 finale says that the SHIELD team will go "to Hell and back." That could be more than just a figure of speech - and they could have help.