I have seen non Catholic commentaries support the interpretation that John is referring to the Christ actually coming as Jesus. I am not necessarily disagreeing with this plain understanding. But it seems to also suggest a possible reference to Holy Communion, no?
For many deceivers have gone out into the world, men who will not acknowledge the coming of Jesus Christ in the flesh; such a one is the deceiver and the antichrist.
It just seems a little funny that John says this the way he does, if he means that some deny that Jesus was the Christ.
On the other hand, is he referring to some Agnostics who believed Jesus was not actually human in nature?