4) Something generally helpful across the board (and which would also help with any of these transitions) would be a warning message when get_property() is called for a nonexistent setting. Currently no such indicator is given.
That is complicated by the fact that underscore preferences not in defaults are removed each day, so at the moment at least it's reasonable to do get_property() on them when they don't exist. I suppose the warnings can be skipped for those setting, though.