Watchtower writers are practised in the art of arguing that black is white. If they were inclined to do so they could certainly make an argument for allowing homosexual marriage. Protestant believers have led the way in this, many of whom now argue that Saint Paul was not opposed to homosexuality as such, but against the casual sorts of relationships common in society at his time. If homosexuals form stable marriages then that could be portrayed as a tolerable situation. Watchtower writers could even claim that JWs and the Bible didn't change, but homosexuals changed and now meet Bible standards. I know that's ridiculous. I'm not saying it's a good argument. But when did that matter in Watchtower land? Or Bible believers generally.
Until just a few years ago the Watchtower claimed the Bible was right when it says "spare not the rod". Now they completely repudiate physical punishment of children and they explain away the meaning of Bible verses that say the opposite. They can clearly do the same again on other issues.
People who argue that the new video and magazine on homosexuality are "nothing new", the Watchtower has always been saying these things and, "how could they have been milder in stating their Bible view?" are missing the point. It's perfectly true that they are just restating their old position that is based on Bible texts. The point is that society has changed and such views are no longer acceptable.
Racism was acceptable and commonplace, until it wasn't. Churches had to adapt or die. Physical punishment of children was acceptable until it wasn't and people had to adapt. Homophobia was acceptable and increasingly it is not. Churches will again need to adapt or die. The change in public opinion in the US on gay marriage is one of the biggest societal changes in attitude ever recorded. Unless there is a dramatic reversal of that trend churches will simply need to adapt to the new situation. Whining that they are only being as homophobic as they've always been will simply not cut it.
What I find fascinating is that JWs are the most homophobic religion in the US according to Pew. This combined with their authoritarian and remote power structure makes them uniquely disadvantaged to be able adapt to the new situation where homophobia is increasingly unacceptable.
What they choose to do over the next 10 years or so will be interesting.