I think swarm hosts might do a solid job of blocking a bioball depending on numbers. Its pretty much throwing up a wall of expendable and relatively quickly replacing pawn blockers to at least give you time to mass your forces together to counter. But I honestly dont know how fast a bio ball will tear through them so take that with a grain of salt. Maybe I missed something, but I dont recall much in the way of new anti air defenses so like you said, a skytoss would probably have a similar level of efficiency against the zerg.