At some point you might as well use Roman characters the way the Cherokee alphabet does - which is to say, uses some of the shapes without paying attention to what sounds they made in English.
I'd expect that Spanish, German and French speakers would benefit just as much as English speakers from these changes.
Its not far off from the union of how all other European languages use the Roman alphabet, would be closer to accurate.
There is no way "every other language already uses the Roman alphabet."
Many languages are internally consistent in how they use it, but those that are aren't consistent with each other. And then there is English, which does pretty much everything any other language which uses the Roman alphabet does somewhere, and probably a few that none of the other extant languages normally using that alphabet do with it, on top.
Additionally, being written in Roman alphabet doesn't neccessarily mean it's clear how to pronounce it. Hungarians calls their country "Magyarország", but unless you know Hungarian, you will be surprised with how it's pronounced. Same as "Chenonceaux", "Tekirdağ" or "Crkvina".
Already done.
- Komen ça va? - Mo byin, mærsi.
We don't have anything against https://en.wikipedia.org/wiki/Louisiana_Creole, do we?
Romanization is, by and large, a thing that exists for people who already know European/Western languages.
But it's a reality that English is the primary (if not sole) focus, for historical reasons and as the global lingua franca. English is taught (poorly, from what I hear) in schools, played on train announcements, is the only Western language available on ticket machines, and is the assumed language of non-Asian visitors to the country. I was even on a couple of domestic flights a few days ago and the captain / FAs made announcements in English. It is not "arbitrary" at all.
Use *h₂enǵʰ-ish please.
English is already heavily Norman-ized. Half of our vocabulary - including the word pronounce - comes from French.
Romanization is an approximation that exists primarily for two purposes: 1. to express Japanese terms in other languages and 2. to enable typing Japanese on a computer. It’s silly to enforce kunrei-shiki, a system rarely used in practice, in the name of "accuracy" based on arbitrary criteria. Romanized spellings will never be accurate for obvious reasons.
Given the purpose of romanization, it’s more practical to choose a system that allows non-Japanese speakers to pronounce words more closely aligned with the correct pronunciation.
Obviously, being more transparent to English-readers is also a reasonable goal a romanization system might have, and if that's your goal the Hepburn is a better system. I don't have a strong opinion about which system the Japanese government should treat as official, and realistically neither one is going to go away. But it's simply not the case that Hepburn is a better romanization scheme for every purpose.
This actually happened in Vietnam, and Korea comes close although they use the Hangul script, not the Latin alphabet.
Kunrei: ki si ti ni hi mi
Hepburn: ki shi chi ni hi mi
The politics of the issue is obviously that Hepburn is older and an American system while Nihon and Kunrei are very purposely domestic (Nihon "is much more regular than Hepburn romanization, and unlike Hepburn's system, it makes no effort to make itself easier to pronounce for English-speakers" [1]). Apparently, Hepburn was later imposed by US occupying forces in 1945.
Perhaps 80 years is long enough and suitable to effect the change officially with no loss of face.
[1] https://en.wikipedia.org/wiki/Nihon-shiki