i dont think it really needs to change. humans have not changed physically, so no need to really change baguazhang.
perhaps the way it is taught may have changed though. many teachers of 50 years ago or before than would teach in just a certain style. some would never answer any questions, or show something just once or twice. it is a bit different now. and the further releasing of info which used to be kept more privately is another difference.
edit: as long as people need to stay fit, or fight eachother, or grow as a person, etc, it will remain relevant.