One potential problem I see is that the Japanese orthographic system is really analogous to an abugida. We often like transforming words in English to fit it to our own dialects. The kana system is rather restricted in this sense. Don't forget about the Norman Conquest, when English was thought, at one point in time, to be mostly French, we keep a lot of orthographic rules, too. In the end, you're describing an orthographic system that would preserve all etymology; this may not work well. There are thousands of languages, thousands of orthographies. In order to maintain the etymological alphabet of every English word, you'd need to make every writer of English Rick and Morty level IQ to memorize the symbols. Moreover, English did used to use more Greek letters (see the old "the" sound in Olde English), but we've manifested this shorter alphabet to account for the most variance in linguistic description. Other than that, miss me with that weeb shit