This ruling will have no effect on the WTS.
<<Suppose a married gay couple, or even one of the partners, starts studying the Bible with JWs and decides he wants to baptized? >>
One has to qualify to be baptized as a JW. Such one as you describe would never be qualified. No legal consequence for the WTS.
The Bible (and thus the WT) does not condemn homosexuality where there is no homosexual activity. It condemns fornication, regardless of whether the one practicing it is homosexual or heterosexual. Anyone practicing fornication gets disfellowshipped.
Many JWs are celibate homosexuals, or they marry persons of the opposite sex. Letters from such ones (some even serving as elders or ministerial servants) have been published in the Watchtower and Awake magazines.
I know of situations where persons of the same sex live together and act just like married couples (for instance, sitting together at every meeting and holding hands during every prayer), and nothing is ever said. If a gay couple wanted to badly enough, it could be done. But, as has been stated already, Why would any gay person in his or her right mind want to be a JW? (Or any straight person, for that matter?)