Feature summary (what you would like to be able to do and where):
Now that the entries of the new vector toolbar have icons (only icon in p-personal-more and icon + text in p-personal) mw.addPortletLink (or an equivalent function) should have a way to specify which icon we want to the new link that just works.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
I want to be able to add elements to new vector's toolbar that doesn't look out of place from the already existing elements through gadgets and personal JavaScript.
Benefits (why should this be implemented?):
Because not having this makes it too hard adding elements in a visually consistent way in the existing toolbar and it's better if getting that visual consistency is worked on in the mw function instead of in each and every gadget that want to add something to those toolbars.