We've already gotten plenty of Minecraft spin-offs like Minecraft: Story Mode - A Telltale Games Series, Minecraft Dungeons and the upcoming Minecraft Legends. And it seems like there might just be a new one coming as well.
As noted by Idle Sloth on Twitter, Microsoft has filed a trademark for something video game related called Ender Dragon. And it seems like this is something they are going all in on as they have also filed the Ender Dragon trademark for "toy figures, books, and clothing" (and even more).
The Xbox team has already confirmed a major Xbox event on June 11, but also said that they have small surprises planned ahead of that. If Ender Dragon is a major stand-alone release, then we should probably expect to hear more in June, otherwise we might get information before that.
Ender Dragon is a flying boss in Minecraft, which is why we believe it's related to Mojang's universe in some way - but it could of course also be completely unrelated.