Yes and No. Hellboy did it with their God-like super villain so I assume it can be done with Ghost Rider, but the movie doesn't have to go in that direction...
In the Darkhold comics Cthon was not really described...we just know he was one f.*.cking evil God and he is something to be afraid of. What I meant with Cthon being the enemy in a Ghost Rider movie was really a reference to the Darkhold.
It would be great to see Ghost Rider have to defeat the succumbed mortals of the Darkhold and in the end have to fight the Demogorge (the Demon Killer who is Cthon's most powerful minion) itself with a violently magnificent epic struggle in the end... Spirit of Vengeance vs Spirit Killer
We can always dream.