The leftist "ideas" that I am beginning to encounter involve their frustration with the basic structure of the Constitution . .in the main body of the text and in the Amendments in The Bill of Rights.
Another thread, current, on this forum touches on the Second Amendment. My PhD (in Education) brother and sister in law both think that education should not be left up to the states. They would prefer, as they put it, " . . .a national Ministry of Educstion",. This attitude or opinion has wider ramifications though. What they really want is for the USA to scrap the Constitution as written and switch to a Parliamentary form of government with strong central control of all aspects of society. They wholeheartedly endorse the European Union and its ability to impose a uniform curriculum on all 28 European Nations. Which is pretty much why Britain "breveted" from the EU.
My recollection is that former President Obama was irritated that the Constitution does not say what the government can do, but rather says what it cannot do. And that was the intent of the Founding Fsthers . . .to limit the power of government and empower the citizenry.
The OP asked for ideas from the left. They will never embrace the ideas of those who fought to throw off a central authority. Tose ideas are somehow foreign to the Democrats. Their ides for government are all at root based on the ideas of Engles, Marx and the globalist-socialists of Europe.