The Fanfic/theory/wish says that drogon will get pregnant, since dragons are nor male nor female, the same time dany get pregnant.

Or even better she has already delivered her egg, somewhere in asshai or old valyria. And no one(not arya) knows about it. Or dany may know about it at the very least.

and the show runner will show us the egg at the end of the series where someone discover them

just a normal/crazy fanfic/theory in my head. but can you imagine if it becomes real or even canon???