I’m not sure you understand MMT. MMT cannot be “implemented”; it’s a descriptive account of how the monetary system functions.
The single basic thing which is completely ignored is that fiat money doesn’t equal welfare. It’s just paper and digits. No matter how much money you print, it simply doesn’t increase amount of goods and services that are for sale.
If you read the article you would know that MMT does not dispute this. I literally say “the government can always buy what is available for sale”. Please actually read the article and/or MMT literature before offering a critique.