> The Latin alphabet does not include J, U, and W, but the English alphabet does (see "Shinjuku")
Japanese does not naturally include distinct U/V letters and does not have a first-class concept that needs to be written with a J; the official way to romanize that place name is "Sinzyuku" and that's morally equivalent to a traditional-Latin "SINZYVKV". W does exist but is decidedly second-class and declining (only the "Wa" sound is really heard any more; I suspect it will go the way of obsolete phonemes like "Ye" and "We" soon enough).
> this would likely be better understood as a form of Japanese spelling reform rather than "Romanization".
It makes no sense as a way of spelling Japanese. It's about standardising on anglicising Japanese instead of romanising it.
Japanese does not naturally include distinct U/V letters and does not have a first-class concept that needs to be written with a J; the official way to romanize that place name is "Sinzyuku" and that's morally equivalent to a traditional-Latin "SINZYVKV". W does exist but is decidedly second-class and declining (only the "Wa" sound is really heard any more; I suspect it will go the way of obsolete phonemes like "Ye" and "We" soon enough).
> this would likely be better understood as a form of Japanese spelling reform rather than "Romanization".
It makes no sense as a way of spelling Japanese. It's about standardising on anglicising Japanese instead of romanising it.