As a native Shanghainese speaker I am extremely confused (and curious!). Cantonese at least has a written form, but Shanghainese AFAIK has no written form, so what does "Shanghainese dialectal spelling" even mean? :\
This article definitely has a political subtext. Spoken Cantonese and mandarin are mutually unintelligible, but in written form, at least without colloquialisms, they are basically the same language. I'm a non-chinese that studied Chinese, so I have no horse in this race. I do think they should support the Cantonese input method, but there's no reason the pinyin method wouldn't work just as well, other than lack of f…
The confusing part for me as a Shanghainese speaker though is that we don't have a way to write Shanghainese, this "spelling" concept AFAIK simply doesn't exist. So I'm very curious to see who actually designed this functionality and what does it actually do.