The percentage scaling ninja markup no longer makes mental sense to me.
[image|300x100,50%] says “show this image (actual size unknown), at 300px by 100px, but wait, scale that by 50%, so show it at 150px by 50px”.
I really don’t understand the point of this kind of notation – because you can just set the pixel sizing however you want it, so why not do the 50% scaling in the first place?
I do not want to specify one display size followed by a second display size, and cannot imagine why anyone would. I just want to say “show this image (of unknown original size) at 150px width, with proportionally scaled height” or “show this image (of unknown original size) at 150px height, with proportionally scaled width”.
I think what would be really great is if we could scale ONLY the width OR the height, and input the word AUTO for the respective dimension.
e.g. Let’s say I wanted this image to be 150px wide but I don’t want to calculate the ratio to adjust the height to the proper resolution… 
I’d love it if we could replace the WIDTH with 150 and the HEIGHT with auto as follows… 