For the first chunk of Season 4, Agents of S.H.I.E.L.D. delighted fans by further embracing comic book storytelling with the surprising and extremely welcomed introduction of Ghost Rider. Gabriel Luna portrayed the more recent Spirit of Vengeance Robbie Reyes, and it wasn't until several episodes in that we learned how he got that way, when it was heavily implied that original Ghost Rider Johnny Blaze was responsible. Fans would go berserk if the hot-headed hero would make a return, but executive producers Jed Whedon and Jeff Bell have some cryptically bad news in addressing Johnny Blaze. From Bell:
There is a tradition within the comics that there's been many Ghost Riders and our take on that was they're not simultaneously a tribe of Ghost Riders but that it's passed. The Spirit of Vengeance is passed from person to person. In that respect, at least our intention was that the Spirit of Vengeance was passed from one person to another. And who passed that on, there are suggestions within the storytelling ... That's as far as we're going to take that part.
So, everything that Jeff Bell said there was both interesting and kind of a bummer. Although it was partly hinted at within Agents of S.H.I.E.L.D.'s Ghost Rider story, it looks like the MCU version can only exist through one character at a time. So if there's only one Spirit of Vengeance involved here, that obviously means we're never going to see any underground Ghost Rider fight clubs, and it also presumably means that if Johnny Blaze ever did get brought into an upcoming episode without Robbie in it, he wouldn't be Ghost Rider.
But that does open up the possibility that Robbie's return in the future, if it happens, could lead to other Ghost Riders coming to power, though in a one-at-a-time succession. (Similar to how the Spirit jumped between Robbie and Mack.) That could be another way for Johnny Blaze to make an appearance, but I guess it's no good trying to speculate about such things.
Frustratingly enough, Jed Whedon and Jeff Bell remained cagey and non-specific about Johnny Blaze actually being the Ghost Rider who passed on the Spirit to Robbie. Bell refers to the "suggestions" made within the show, such as the leather jacket and motorcycle, as well as the Quentin Carnival poster that popped up. If there's no plan to refer to that character again by any name, then why keep all the secrecy up? Perhaps that potential standalone Ghost Rider project started moving forward, making namechecking characters more difficult.
Of course, Jed Whedon did offer up a particularly cheeky exemption to their claims. Here's what he told IGN in reference to Bell's explanation.
If we find a story where that's not true, we are going to go back on that in an instant.