As author of Safari User CSS extension[1], most of support email I've ever got are from non-developers. There are many kind I can recall, from those who simply want to adjust font sizes of a site permanently, to following tutorials on website on how to customize YouTube layout, to those that wrote userstyles on their own. I even got questions like "how do I turn Google black"/"how do I remove x from this url" sometimes.

I'm not sure about Chrome, but Safari had a similar feature but it lacked a way to scope stylesheets to certain domain. If Chrome userstyles behaves the same way then I don't think this change will affect those users anyway since being able to scope userstyles to certain domain seems very important to them.

[1] http://code.grid.in.th