Can you think of any domain of application, other than 2D images, where it could make sense to use max pooling or convolution?
Because the ONNX format allows for non 2D inputs. On the operators page (https://github.com/onnx/onnx/blob/master/docs/Operators.md#MaxPool) they say
dimensions for image case are (N x C x H x W), where N is the batch size, C is the number of channels, and H and W are the height and the width of the data. For non image case, the dimensions are in the form of (N x C x D1 x D2 ... Dn)
And I did a search, and couldn't find an application where non images.