Weapon wall could mean when you've got a weapon braced against a railing. Maybe they're looking in to that. Or maybe they're talking about quad-guns. Or maybe cap points and fortress are going to get like, rows of shootahs and bolters and stuff stacked together in a giant wall of dakka. Also the minute I saw the Damned Legionnaire, this is what came to mind. And now I can't unthink it. Foul Xenos!