One development in the original Ghost Rider franchise essentially makes Nicolas Cage unusable in the MCU.

SUMMARY

Nicolas Cage’s Ghost Rider might confuse fans if he makes an appearance in Secret Wars.
By the end of Ghost Rider: Spirit of Vengeance, Johnny Blaze’s flames had turned blue, which did not have as much time to sit with the audience.
Secret Wars could bring a different version of Johnny Blaze into the MCU, one who still retains his blue flames.

Rumors about Avengers: Secret Wars claim that a slew of non-MCU Marvel heroes will be making thier appearance in the Marvel Cinematic Universe. Among them is Nicolas Cage’s Ghost Rider, the Spirit of Vengence who starred in two films playing the soul-taker from hell. Among Ang Lee’s Hulk and 2005’s Fantastic Four, Cage’s character is now one of the front runners that fans want to see in Avengers: Secret Wars.

Nicolas Cage as Ghost Rider
However, these plans need to be executed carefully, given that Secret Wars would need a cameo from Ghost Rider, The Spirit of Vengeance. It needs to be the iconic skull and flames that fans are familiar with, which might spell doom for those expecting to see Nicolas Cage. This is because in Ghost Rider: Spirit of Vengeance, because of the way the story unfolded, Johnny Blaze is actually the Spirit of Justice, with Blue flames.

As of Spirit of Vengeance, Ghost Rider has blue flames.

Ghost Rider: Spirit of Vengeance (2011)
Ever since the events of  Ghost Rider: Spirit of Vengeance, Johnny Blaze has been the Spirit of Justice, with his flame being blue instead of the usual orange and red. This was to signify that Johnny Blaze no longer had any connection with hell, and was a servant of God now, with his body being encased in the much more powerful holy fire rather than hellfire.

Therefore, if this Ghost Rider was to make an appearance during Secret Wars, it would not only confuse fans but also overly complicate the plotline. While a simple cameo won’t hurt anyone, having this version of the Rider feature heavily in the story could cause a slew of issues, narratively speaking. However, there is a simple solution to this issue, one that has already been implemented multiple times in the MCU already.

Nicolas Cage from Ghost Rider could show up instead of the one from Spirit of Vengeance

Nicolas Cage in Ghost Rider
The X-Men that we have seen so far in the Marvel Cinematic Universe have all been from alternate realities. However, they do not seem to have the remnants of any of the adventures they had in their own films, leading to the idea that they might just be adjacent to the Fox X-Men rather than being themselves. This is also corroborated by the fact that the X-Men in the MCU seem to be a fusion of the X-Men in Fox’s films and X-Men: The Animated Series.

Similarly, if Ghost Rider has to be part of Secret Wars, and it has to be the Nicolas Cage version of the character, then the one that shows up in Secret Wars could be the Ghost Rider from the first film, instead of the one that has already become the Spirit of Justice. The upcoming Deadpool & Wolverine may set the precedent for how characters from other universes are going to be treated in the Marvel Cinematic Universe.