It's part of a government initiative to improve English throughout the country, in response to reports that Japan is close to last in a long list of countries in terms of English ability.
There are a number of reasons why introducing these classes is a terrible idea.
For starters, for the most part homeroom teachers will be teaching these classes, using the new "Eigo note", a simple curriculum designed for the purpose. A recent survey has shown that the majority of homeroom teachers lack the confidence, ability or training to do these classes. In fact, they would prefer if the classes were taught by EFL professionals. Nevertheless these homeroom teachers will be forced, many against their will, to teach a language which they cannot, for the most part, actually speak, and which they may not have studied themselves for several decades.
Ministry of Education officials stress that the "Eigo note" will not be teaching comprehensive grammar rules, but instead greetings, games and self-introductions. I am not convinced. The title itself is enough to make one wary: 'note' (meaning 'notebook) is a particularly pernicious example of the false translation that goes unchecked in Japan; its inclusion in the title does not inspire confidence in the rest of the material.
The introduction of these classes are sure to undermine the good work that foreign ALTs have been doing in elementary schools up to now. Unlike in junior high and senior high schools, until now JETs have had most responsibility for and input into elementary English classes. However, JETs can only visit one school a day, and have several (even up to 10) elementary schools to visit, plus junior and senior high schools. A typical JET may visit a school twice a month or less. This means that their teaching will now be undermined by the Japanese homeroom teachers, who will be using 'Eigo note' for their own classes, or even forcing it onto the JETs, who may or may not want to use it. They certainly should not be forced to, as the typical JET has the enthusiasm, if not the experience, to teach other stuff. Not to mention their own materials. However the threat that Eigo note will undercut what good work has been done until now is very real.
The main problem with these classes however is that they are not addressing the real problem. It doesn't matter if you give the kids 1, 2, or 2,000 classes a week in English. The system is garbage. Serving up yet more garbage is not a viable solution. The answer is to not serve garbage in the first place. When these kids get into junior high, even if they can use greetings, numbers, days of the week etc naturally, they will have the beating heart of their motivation ripped out of their chests by the jagged rusty machete of the junior high English system. Soul-destroying grammar drills, months of dry exam preparation, no actual English usage...
Like many Japanese initiatives, it is all form and no substance.