I think there’s a few things to consider with this.

Number one is your commitment. The thing about traditional learning is that there’s a nice, soft, on-ramp for newcomers. Textbooks are written in English with Japanese examples. Services like WaniKani also use English to introduce new words and kanji. If you take a class, your teacher will use English to explain things to you. If you’re new, this is a far more comfortable process because, well, you learn slower and you likely have a clearer understanding of the things that you learn as they come up. I think this helps keep a newcomer motivated.

If you’re not committed or motivated enough, I think this total immersion thing is going to fail real fast. It’s going to be really challenging and likely very frustrating, and if you’re not willing to get through that, you might get burned out and stop before you’ve made any decent progress.

Number two: I’m not convinced that the average person can climb that vertical rock face that is total immersion without at least some basic equipment first. I think you need to have some vocabulary and some grammar under your belt first. Like, if you don’t understand the が particle or です or those most basic grammar points, you’re lost before you can even begin. I just can’t imagine someone can learn from this process without at least understanding some basic sentence structure first, and I think you need a bit of traditional, textbook style learning to get to that point. Hell, even if it’s a radically simplified textbook style, like WaniKani or Bunpro- doesn’t necessarily have to be Genki.

Number three: I think you need to have some context to your listening practice first. Using subtitles, for instance, is a crutch that should be dropped as soon as possible, but I think it is necessary for a short period that you get some listening practice in while understanding what’s being said. I think subtitles are good for this, I also think hearing voiced examples in your practice is good too, whether that’s Genki readings or the spoken vocabulary in WK or even just YouTube lesson videos.

I think this total immersion process is useful for two things: picking up new vocabulary, and getting a better feel for how people speak conversationally. Vocabulary is something you develop over your entire life, even in your native language, and the only way to successfully do this is to regularly speak with others and consume content in a language- specifically, have conversations and consume content that is maybe a bit more specialized or a bit outside of your sphere of knowledge. I think immersing yourself in a language therefore will help you accomplish this goal.

You also need lots of immersion to become fluent, without a doubt, especially conversationally. This conversational fluency is obtained through immersion in two ways: frequent examples, and frequent reinforcement. You will pick up on common words and phrases and have them used in examples, contextually, through immersion. This is fantastic, since if you’re just studying vocabulary, you may not get these examples. Second, for words and phrases you already know, immersion’s going to continuously reinforce those words and phrases in your mind. One big issue with traditional study is that you need to be self-disciplined enough to regularly review your material because if you go too long without it, you’re going to forget it. Immersion will fill that role of study reinforcement naturally, especially if you’ve successfully studied common vocabulary.

That was a lot. Here’s my short opinion: immersion is great once you’ve passed a certain threshold with traditional learning. I think you need to get through a textbook or two and get a few thousand words under your belt first. I think without some basic understanding, you’re setting yourself up for frustration and failure. However, once you have that, I think immersion is potentially the best tool for further development and reinforcement. It’s more practical, it’s more “fun”, it’s more natural, and it helps develop skills you just can’t get from textbooks and flash cards.

One final note: all Japanese, all the time is basically an unattainable goal unless you live in Japan. If you live anywhere else, most everything around you will be in your native language. Here in the US, for instance, everything I see is in English, every conversation I have is in English, I have to actively seek out Japanese material if I want to study it. If you have a job, if you live with English speakers, I think this is impractical. Given the current state of the world, if you’re spending most of your time at home, this is probably the best opportunity you’ll ever have to attempt this and I see no reason why you shouldn’t try- just don’t get frustrated if it’s not possible and don’t neglect anything in your normal life in favor of this process. If you have school or work or a family, you’re going to have to speak in English. You can, of course, attempt to make all of your media consumption Japanese though, I see no reason why you shouldn’t do that.

I think setting attainable, reasonable goals is far more effective, hence why I wouldn’t ever recommend total immersion to someone with no knowledge of a new language whatsoever. Be proactive, challenge yourself, but be realistic. 100% immersion isn’t practical for many reasons.

Of course, this is all my opinion and I have no doubt that it’s doable for some people, I just personally can’t imagine this working for most people.