Apparently, in "The Structure of the Japanese Language" chapter 8 page 119, Kuno asserts that the following is grammatical:
John wa Tokyo ni ni wa itta ga, Osaka ni ni wa ikanakatta
I have a few questions. Firstly, what triggers this duplication? Secondly, what difference would it make if we were to replace にには with には? Kuno does not really go into too much detail with regards to this particle duplication phenomenon; however, he provides quite a few examples of this phenomenon, but nothing more than that. I have not seen or heard this type of construction before, but I would appreciate any leads (perhaps a relevant paper) greatly.
Update: Kuno says that the presence of は triggers the duplication (?)