Hi EdenOne,
Interesting observation.
Moreover, no man has ascended into heaven but he that descended from heaven, the Son of man - John 3:13 NWT
No one has ascended to heaven but He who came down from heaven, that is, the Son of Man who is in heaven - John 3:13 NKJV. Includes a footnote on regarding who is in heaven.
No one has ascended into heaven, but He who descended from heaven: the Son of Man. - John 3:13 NASB
and no one hath gone up to the heaven, except he who out of the heaven came down -- the Son of Man who is in the heaven. - John 3:13 YLT
No man in existence has gone up to heaven, except the Son of man who has come down, whose home is heaven - Your suggested translation.
AND(kai) NOT-YET-ONE(oudeis) HAS-UP-STEPPED(anabebEken) INTO(eis) THE(ton) heaven(ouranon) IF(ei) NO(mE) THE(ho) OUT(ek) OF-THE(tou) heaven(ouranou) DOWN-STEPPing(katabas) THE(ho) SON(huios) OF-THE(tou) human(anthrOpou) THE-One(ho) BEING(On) IN(en) THE(tO) heaven(ouranO) - http://www.scripture4all.org/OnlineInterlinear/NTpdf/joh3.pdf
One of the problems with your suggested translation is the verse does not contain the Greek word for "home". John 14:23 has the word "home", as per scripture4all.org it is the word "monEn" which is translated as "REMAIN", but also as "abode."
Certainly, it is easy to see why NWT would prefer to have the "who is in the heaven" reference removed from the verse, since as you point out it could be used to support a divine nature of Jesus being both on earth and in heaven at the same time. If one reads the verse as if Jesus is speaking each word to Nicodemus, then this "in the heaven" could be problematic. However, if one simply suggested the "in the heaven" is an after-thought added by the author of John it could be addressed in that way. Especially considering John was written long after death of Jesus.
Does this verse support the idea that Jesus is saying no person on earth had gone to heaven, as taught by Jehovah's Witnesses? Maybe, but I don't think the verse absolutely requires that. 2 Kings 2:11 contains the account of Elijah who it is said ascended in a windstorm to the heavens. There is of course many folks who have addressed the John 3:13 contradiction of 2 Kings 2:11. Personally I think the least expensive way is simple to say the author of John wasn't thinking about the Elijah account at the time. In fact we know what the author of John was reflecting on, because it is in the very next verse...
And just as Moses lifted up the serpent in the wilderness, so the Son of man must be lifted up, 15 that everyone believing in him may have everlasting life. - John 3:14, 15 (see also Numbers 21:9).
So... the emphasis is not just where Jesus was (heaven) and was going (also heaven), but on the katabas and anabebEken (descending and ascending). That is, the ascending of Jesus was the key thing for Christians to look to, like the Israelites that looked up to the copper serpent. My view is the ressurection of Jesus was both a difficult doctrine for Christians to accept yet at the same time a primary to the faith (1 Cor 15:12-14). The next verse of John is one most often cited by Christians, namely John 3:16. In contrast the most often cited scripture in Watchtower publications is Matthew 24:45 ;-)
Cheers,
-Randy