It'd be sweet to be able to insert thumbnails of images instead of only being able to insert the full-size image.
Ideally, you'd just have an option in the "Image Properties" dialog:
[X] Pop-up from thumbnail of size: [________________]%
Then the wiki would show the thumbnail in-line (with the same alignment options) and show the full-screen-sized image in a lightbox when the thumbnail is clicked, with an option to show the full-resolution image in a new window/tab.
Even if I have to generate the thumbnail myself, you could do something simpler, like adding an option to the "Image Properties" dialog:
[X] Link from thumbnail: [________________] [Choose File...]