First of all, you need to take this rumor with a grain of salt.
According to GamingRumours, ‘Ryse: Knights of England‘ would be the sequel to the upcoming (and still unreleased) ‘Ryse: Sons of Rome’ for Xbox One. Crytek could be waiting to see if Ryse: Son of Rome sales prove fruitful on the console and, meanwhile, would be already planning a sequel set set in Medieval England that includes dragons.
VG247 contacted with Crytek and a rep told them “we don’t comment on these kind of rumors”.
I would just like to note just one fact: Crytek spoke about Crysis 4 before Crysis 3 released.