1. 10 classes is way too small to make meaningful estimates as to how well a model will do on a "proper" image datatset such as COCO or ImageNet. Even a vastly more complicated dataset like CIFAR-10 does not hold up.
2. I feel like CIFAR-100 is widely used as the dataset that you envision MNIST-1D to be. Personally I found that some training methods will work very well on CIFAR-100 but not that well on ImageNet so TinyImageNet is now my go-to "verify new ideas dataset"