Might be that the gun isn't a priority right now. They've saved the space for it in the location marked by Blitzo, but they didn't install the gun yet.
Very doubtful, the gunport is not something you just add on after a plane has left the factory, especially in a stealth fighter.
I'm also a little bit confused, are you suggesting that we should expect to be able to see the gun port in an obvious way?
Because don't get me wrong, maybe J-20 doesn't have a gun, but everyone seems to be thinking that if a gunport was present then it would be super obvious and easy to see, and using that as the main argument for suggesting J-20 may not have a gun.
Remember, this is a stealth fighter, and a quite voluminous one at that -- so if anything, we can reasonably estimate that if J-20 does have a gun, then the gunport will probably not be obvious to see at all (like on the F-35A), and will likely be more like the F-22's gunport, which is almost impossible to locate unless one already knows where it is.
So saying "we can't see the gunport" right now is probably the worst way of arguing the position that J-20 does not have a gun, because considering the type of aircraft J-20 is, and considering the gunport on a similar aircraft (F-22), then we should
expect the gunport to be virtually impossible to find on J-20.
/rant over
