Just found this thread, and this feature is absolutely awesome!
Check out www.imgur.com for multiple-image uploading done right from the user's perspective. In this case, I think sacrificing "pure" HTML for the ability to upload multiple files at a time may be necessary.
Don't know if someone said anything but I did notice in the video that when you have taken up the entire space of the editor you have no scrollbar appear but you can still scroll it.
Otherwise, great feature, I'm anxious for this now.
I'm talking more about how the upload form functions. You can select multiple files in the file select dialog, when you click OK it lists those files, and it's one button to upload them all, with a progress bar. Simple, clean, fast.
I had a similar idea that I've been giving some thought.
When I have some time I will also take a look at plupload, though you must understand my reticence to integrate such a tool is based only on my lack of experience with the platform, which could potentially result in me being unable to offer meaningful support to my customers.
Improved image support system wide(when CMS and Blogs come to term here) would push me in the direction of getting XenForo.
IPB does a lot of things great and they are always thinking ahead, but in the conversations I have had over there about the handling of images it sure doesn't seem to get any interest, which is ashame because I know they could do a good job of it.