You have provided a good summary of the submitted article, without expressing an opinion on its conclusions. Allow me to respond to quoted point 2.
2. Low immigration - so "Finnish as a second language" is not a problem there.
A counterexample to this being especially important is the country Singapore, with four official languages (Modern Standard Chinese, Malay, Tamil, and English in decreasing order of number of home speakers) from four different language families. Especially important to consider is that English has been the sole language of school instruction in Singapore during my lifetime, even though essentially no one before the current generation of young graduates grew up in an English-speaking home. Moreover, Modern Standard Chinese ("Mandarin," called 華語 in Singapore) was not the home language of the ethnic Chinese majority of the population in Singapore, but rather Hokkien or other south Chinese languages that are as different from Mandarin as English is from German. (I speak much Mandarin and some Hokkien.) MOST students in Singapore for more than a generation were learning their school language of instruction as a second language as they attended school. (This was true of my wife's generation in Taiwan too, where Hokkien, "Taiwanese," was the home language and Mandarin the school language.) United States, and maybe British, teachers put a lot of blame on immigrants for not growing up speaking English, but an effective school system can handle a multilingual surrounding cultural environment and still DEAL WITH IT while helping the learners learn the preferred official language. See the TIMSS report
http://nces.ed.gov/pubs2009/2009001.pdf
for the consistent finding that the average level of Singapore pupils in mathematics is comparable to the "gifted" level of United States pupils. The population of Singapore was not selected for high IQ or high levels of schooling (the immigrants who settled Singapore were mostly indentured agricultural laborers who fled wretchedly poor parts of China or India) but today's inhabitants of Singapore show the results of sound education.
4. And contrary to all our K-4 efforts, kids don't start school to 7.
Agreed with your noting of point 4 as an important issue, distinct from United States policy proposals.