From a very quick cursory look, Japanese seems to have some sort of commas and periods. Shouldn't it be just simple to adopt spaces, (and proper commas and periods and parentheses, which they actually use already) too?
Many all-kana texts employ spaces. All-kana with no spaces is a nightmare.
On one hand, language has always been an amorphous thing and has changed throughout history. On the other could some changes change the very nature and heart of it? No one agrees on those trade-offs, and I argue likely never will.
This has been always the case. I mean, think of how modern latin letter forms developed. Think back to the Roman Empire, when the letters were etched in stone or wax tablets, with only capitals (before the invention of minuscule), drawn with straight lines that are easy to chisel. Think of the later periods when many books were written by scribes using pen and ink, resulting in changes to letters so they could write entire words in one hand motion. Later still, we have the printing press and its demands that each letter be a discrete unit, doing away with the wavy flow of words. Today most people write using print letters simply because the majority of writing you would encounter is in print, so that's what's easiest to read. Those changes probably don't register to you as egregious as the one parent proposes, due to the fact that the person enforcing the change and the person developing the technology are one and the same - a native speaker modifying his own language to fit the tools at hand. Which I think brings us to a resolution - the native speakers of the language are the ones to decide how to change it to suit their everyday needs, including making it easier to produce and consume with the tools of the day.
Agree with you here, it's well outside my rights as an English speaking American to have an opinion of any merit. However I would still struggle to call handing it over to native speakers a resolution. Many native speakers have incredibly strong feelings on both sides of the argument; and often for very good and valid reasons.
I'm glad the Unicode Consortium exists, because I am CERTAIN I don't want to be the decider or facilitator of these discussions. Way above my pay grade.
To choose some random capital Roman letters, how about... SPQR? Those got inscribed all the time.
Roman letters don't really show any bias towards straight lines. Don't confuse the fact that we split the Roman letter V into two letters U/V with the idea that they didn't carve curved letters. Check out this awesome plaque from the year 90: https://www.timesofisrael.com/in-a-bronze-inscription-a-remn...
Don't leap to conclusions about the benefit of breaking up the text. For example, reading Mandarin pinyin is much more difficult than reading characters, but neither of those involves a mixed script. (And heck, the pinyin might have word spacing! [1])
The reason is pretty obvious - characters contain a lot more than just phonetic information. That makes things harder on the writer, and easier on the reader.
[1] Pinyin produced for foreign learners usually has word spacing. Pinyin produced for Chinese children usually doesn't.
This cannot actually be true; the spoken sentences do not indicate word breaks, but grade schoolers (and toddlers) can parse them just fine.
The most obvious way to see this would be to think about synthesized speech, which almost never uses natural prosody. Think of the voice of Stephen Hawking, or just a splicing of some prerecorded options. ("At the tone, the time will be / TWO / TWENTY / THREE / and / TEN / seconds.")
I think having spaces is useful, too, for learning speed and expression.
Early Japanese on computers also used half-width kana but now it's all properly fullwidth.
Don't mistake technical limitations for choice.