Japanese as it currently exists is just really hard to read when written without kanji. A couple reasons: it has TONS of homophones, and it doesn't use spaces, and also it has lots of common words that are only 1 or 2 characters long. So if you're parsing a stream of kana, in the general case there will be several different ways to interpret the next couple characters and you'll constantly be backtracking.

So at a minimum, dropping kanji would mean the language needed to develop a system for where spaces go (which is less trivial than it sounds IMO). But also it would need to abandon a lot of homophones or find some way to disambiguate them. It could happen I guess, but I'm not sure how it could happen gradually.

I don't know if this is from the perspective of having learned Mandarin in elementary school first or if Japanese folks feel similarly, but reading words like, e.g., だいがくいんせい versus 大学院生 is actually a little more annoying because I have to scan more of the line to read the word in question. This is notwithstanding the effect that hiragana has in highlighting grammatical structures; it's a lot like setting off Finnish case endings and verb conjugations in a different color.

At least, that's the reason why I prefer still having kanji around.

Well the "native syllabary" is derived from Chinese characters, it's not something that was there and then Chinese characters were shoehorned in later.

I think at some early point most Japanese learners (that don't already know a Chinese language) think kanji should be dropped. And at a later point I think most would change their mind as the advantages outweigh the disadvantages.