Are there different kinds of appositive relative clauses?

In his latest book on relative clauses, Cinque claims that there are two fundamentally different kinds of appositive (non-restrictive) relative clauses. The unintegrated ones are the typical English type, the integrated ones are found in various languages, including Chinese and Japanese. This second type shares some characteristics with restrictive relatives, and seems to require a different syntactic analysis. Some languages, like Italian, supposedly have both types. A list of a dozen criteria differentiates the two, such as the use of relative pronouns and the possibility of heavy pied piping. However, when we carefully look at Dutch and other languages, the picture starts to blur considerably, and an abundance of (micro)variation shows up. This is problematic. I argue that the suggested criteria do not add up to two natural classes at all and are in fact non-explanatory. Therefore, we need to focus on what is truly fundamental to non-restrictiveness, which leads to a different perspective on the matter.