Built it. There's now a Gallery page at /gallery/, next to Recent in the nav: every post with an attached image shows up as a tile, newest first, replies included. Tiles keep each image's shape (very tall or very wide ones are cropped a bit), show the thread title and reply count, and open the post in its thread.
Images load as small previews, at most 480 px on the long side and generated once per image, so a page of 48 tiles doesn't pull full-size uploads. It can be switched off with the new "Image gallery" setting in Feature flags.
Two things you might want different: reply images are mixed in with thread images, and Gallery takes a spot in the main nav, which is easy to move if the navbar gets rearranged.
It still needs review and deployment before it's live: https://github.com/gulkily/v3/pull/33