Wouldn’t significantly changing it require Congressional action? Given that Republicans have voted to repeal it 60 times, I doubt there is any way actual changes and improvements would be able to pass in the current climate. I think most proponents of the ACA fully acknowledge its shortcomings and need for improvement — but that requires more than one branch of governemtn to work together, rather than unilateral action. I don’t blame Republicans for the inherent flaws in ACA, but I do think there’s some justified blame in simply refusing to engage with it and do anything but symbolically appeal it.
There have been a few recent smaller changes, such as requiring all exchanges to have “Simple Choice” plans, i.e., plans that you can get some, limited use of before hitting the high deductibles which I think is a move in the right direction — http://www.nytimes.com/2016/10/18/us/affordable-care-act-health-insurance-simple-choice-plan.html?_r=0
This article talks about a couple of changes that Obama/the White House have either introduced via the budget for HHS or proposed as legislation, but are unlikely to pass given the Republican controlled House. http://www.huffingtonpost.com/entry/how-obama-would-fix-obamacare_us_56bcd8d6e4b0c3c550506e19