It doesn't matter what the scriptures say about booze, they could ban it if they so choose. Just because it says it'll be there in the new system, or because Jesus made wine, it doesn't mean that we have to drink now.
Just like beards - the only relevant scripture in the bible goes directly opposite to their ban. They've even speculated (or told the story of someone that speculated) as to whether men would wear beards in the new system. This would just be the same thing - Oh we can have wine in the new system because there will be no chance of stumbling anyone and we'll be perfectly able to resist the temptation to overly indulge. But for now, we have to make ourselves extra pure and go above and beyond and be faithful in what is least, etc etc.
That said, I doubt they'll completely outlaw it. As things stand it can be a useful tool to judge people and build different tiers of JWs. JWs love to rank themselves so that elders and pioneers can feel superior to other JWs. They can use it as a secondary means of judging people - if you don't want brother x to be an elder, suggest that he drinks to much. They also don't want to lose more members, so they'll be unlikely to start DFing people for drinking, so they'll likely continue to try to walk the fence like they are now - it's the perfect solution. Impose control on the JWs that are most 'in' and get them to stop drinking. Let the others that continue to drink stay donating JWs, but impose a guilt trip on them to keep them feeling like shitty people.
