Things to try:
capsule layers (hard) - https://medium.com/ai%C2%B3-theory-practice-business/understanding-hintons-capsule-networks-part-i-intuition-b4b559d1159b
improve Wasserstein GAN (current version, easy) - https://arxiv.org/abs/1701.07875
use DCGAN (medium) - https://arxiv.org/abs/1511.06434
solve gray background problem (~)
implement Conditional GAN (medium) - https://arxiv.org/abs/1411.1784
Use different dataset:
mnist
CIFAR-10
CELEBA
and many many more: http://deeplearning.net/datasets/