You can always corpserun though, or just not ress if the situation is that bad. Gotta admit that I thought this was in 20-29 section writing my earlier post, and 20-29 players are on average so shit that you can leave the bg with ease anytime you want. Not the same for 19 obviously so my bad.
My point anyways was, that unless it's a premade, the outcome will probably 99% of times be the same if there were walls or not. Some turds would keep running into enemy team bravely, dying every time but never giving up. Then there's gonna be a few people QQing in bgchat and not ressing, and a couple guys who just stealth around the map being useless or trying to solo the EFC / solo carry the flag with futile efforts. There's a big chance the team wouldn't really leave the GY again that game, due to the fact that they got overpowered so hard by the enemy team in the first place.
If however it's a premade team, or just a strong team with good co-operation, and have a comp strong enough to stand against the enemy team, they would eventually break free from the GY whether there were walls or not.
I guess the walls could make a small difference, but IMO it would be pretty damn marginal. Just my thoughts about it though, and since I've only ever played EU, my view on the bracket might be biased since I don't know exactly how bgs are on US. I guess we'll see when/if it comes out if it actually makes a difference in the outcome of games...
Oh yeah and obviously if they make it so you can execute some OP jumps to and from top of the wall, it could be really gamebreaking and change wsg meta quite a bit, but I honestly think they're gonna make it more or less unclimbable.