The switch to Hepburn rules is reasonable since it's the de facto style of romanization but, if they were going to go thru this sort of effort to revise their written language it seems disappointing that they wouldn't add stress marks / accent marks to their romanization. It especially makes sense in Japanese to remove ambiguity like, 港南. Konan, naively in Hepburn. But is it Kon-an or Ko-nan? Kònan removes ambiguity.
Given that the "Ko" is actually pronounced "Kou" (i.e. hold the "o" sound for a beat longer), I'm not sure how the downward accent helps? The bigger thing than "kon an" vs. "ko nan", IMO, is that the romanization rules don't capture these kinds of repeated/extended vowel combinations. Honestly, anyone who is sufficiently capable in japanese to know that 港南 is something close to "Ko + nan" is going to know hiragana an…
That would be lovely and possibly and attainable goal for a minimally tonal language like Japanese, but the challenge is generalizing any such system to heavily tonal languages like Hokkien, with six or seven tonal markings and additional layers of complexity like tonality rules that depend on different word boundaries and positions.
It's a shame that different shades of ink weren't invented and/or normalized sooner, because a lot of this state space could be captured using a simple convention of two stroke weights (light/heavy) by two shades of color (red black) for every glyph.
"Rubric" was an early gesture in this direction but unfortunately never escaped its original application.