I think it is clear that there are Servoy developers who are quite interface conscious and are pushing the envelope in this area beyond what many thought was possible with Servoy. If this feature is eventually implemented, you will get better functioning applications as a result.
I completely agree with David, if your interface is important to you this feature should be available. Why did Servoy implement setImageURL without the corresponding setRollOverImageURL, as you can set the rolloverimage from Developer?
Again the question to the Servoy people: any progress in this area?