Hi Hitoshi,
The plan is to keep the Image Gallery portlet the way it is right now from a user experience perspective. But it will be reimplemented as a "display" of a folder of in the document library.
The overall idea is that you have one unique library and then allow developing several portlets that show different views of it, for example to offer an optimized experience for specific file types such as images, video, sound files, etc.
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