we should really implement this

I still find it fascinating that after all this time, and despite this experiment being relatively well-known, there seems to have been no real equivalent since then. I think there are political hurdles to implementing something like this (particularly given the current bent, at least in the US, toward standardized testing, and the current state of those standards), but I think they are not insurmountable. Jo Baoler describes promising results in this paper (under the heading "EVIDENCE OF EQUITABLE TEACHING "), though even that was nearly 15 years ago and seems not to have "caught on."

not only with one language, but we should start teaching foreign languages to kids as soon as possible

That's really interesting, and something I hadn't really thought of before (at least not insofar as it relates specifically to Benezet's curriculum). It seems logical to me that learning a second language is beneficial to young students, even if they don't make much practical use of that language later in life. I'm not familiar with any research in this area, though; I think it would make an interesting experiment!

On my more radical days, I might argue that we should get students started from that young age not only with additional natural languages, but also with programming languages...