I would argue that it could be possible of a fourth film. Hell, KFP; which was lower than any of the others has been said before that a sequel to the trilogy could happen, and that I wouldn't see that as an impossibility for Dragons.
Not to mention, this IP; is stupidly easy to have for IOA, as it fits so many requirements.
- Great Environments that would blend extremely well for a land
- Actually was based off of a book
- Popular on Netflix, with a third film coming out in 2019
- Has multiple different opportunities for attractions
- Merchandise opportunities are endless, especially of doing custom dragons to compete with Pandora - The World of Avatar's Banshee's
- Has already had a tested arena show that went on tours across the globe (Not to mention Creature Tech having a hand to play in the development of that show)
- E.T.C.
There is so much they can pull, and that while a part of me wishes that it's saved for Gate 3, this would be the best replacement for Lost Continent.