A button to place the image in the post would be just about it. I am hopefully going to change from Phorum to Vanilla when it feels robust enogh and our current "inline images module" has that function and it is very popular. Something like this:
filename [delete] [place in line]
Just a suggestion on how to make a good extension even better!
jomper!! Great idea!! I will implement such a thing in my next release :)
Also, Vanilla is VERY stable. It's just some extension collide with eachother... Attachments and Inline Images are quite robust, although not all servers seem to be happy with the file uploading/writing... that's something you'll have to test for yourself.