I dealt with this quite a bit and recently consulted for a friend wanting to do something similar. The issue is you think you can drag and drop data fields and

I dealt with this quite a bit and recently consulted for a friend wanting to do something similar. The issue is you think you can drag and drop data fields and be all set. But to deliver a halfway decent UI, you need custom bits and pieces here and there. From layout, to extra JS, to new "picker" types for some fields, and on and on. When I've looked at it, the issue is either the forms toolkit gets stupidly complex or doesn't have a good customizability story, and in frustration you throw away the toolkit and just do it by hand. There's room to do something better, so long the customization is really easy and trivial to add one-offs.