Is your feature request related to a problem? Please describe.
Currently, we already added support for customized writers in SaveImage transform:
https://github.com/Project-MONAI/MONAI/blob/dev/monai/transforms/io/array.py#L344

I will add a similar logic to the LoadImage transform for customized readers.