This is a very important fix. Although we always put image placeholders in our templates that indicate the exact dimensions that a user should replace them with, these are often ignored or users are unsure what the parameters mean. As soon as these image dimensions are modified it completely throws off the responsiveness of an email, and its easy for a user to accidentally do.
Happy to hear that you are making some changes soon. Are you able to give us some insight into when we can expect these changes to happen so we can in turn communicate those dates to our Marketo clients?
Also, is it possible for you to ensure that the height field is NOT mandatory for any images inserted into templates? This was never the case previously in Marketo, and it wreaks havoc with all fluid or fluid-hybrid templates.
Or perhaps mktoImgHeight could be set to "auto" which would prevent the height being mandatory.
After the upcoming release, you can use mktoLockImgSize to lock "height" and "width" properties of the <img> in an image element. Likewise, you can use mktoLockImgStyle to lock the "style" property of the <img> in the image element.