It's currently impossible to open a Nifti2 image. I only tested on Windows 10 (MITK 2016.11 and 2018.04) but it probably affects all OS.

3526.53 core.mod.core.ioUtil ERROR: No reader available for 'path/to/nifti2.nii.gz'

I created my images with this python code

import numpy as np
import nibabel as nib

data = np.random.rand(4, 5, 6, 7).astype(np.float64)  # or any other type
affine = np.eye(4)

nib.save(nib.Nifti1Image(data, affine), 'nifti1.nii.gz')
nib.save(nib.Nifti2Image(data, affine), 'nifti2.nii.gz')

I know that VTK supports it since 6.2 so I think MITK should support it.