The future of the democrat party

In 2008 there was a wave of populism towards Obama unlike anyone in a long time.  It was very easy to see where the Republicans were doomed going forward because they truly were out of touch with the people.
However, over time the Republicans went to work and started seeing what people really wanted and slowly but surely started whittling their way back into relevance.  In the mean time the very popular populist Obama was turning more and more into "just another big spending politician" and the economy was sputtering.
Then insert a new candidate with an equal wave of populism in 2016 and the tide of the people had shifted.  I don't believe there was a huge ground swelling of far left people supporting Obama any more than I see a ground swelling of far right people supporting Trump.  It's the people in the middle who simply wanted change in 2008 are now wanting change in 2016.  If Trump turns into "just another big spending politician" and the Democrats seek out the populist message then the tide will surely shift again.

Unfortunately for the Democrats I feel that they're acting as though Obama won on a wave of far left issues and support because they seem to be doubling down on the fringe issues and completely ignoring the populist demands.  As the article you linked shows they're even going so far as to essentially evict anyone that doesn't have a fringe view on the platform topics.  If they continue down this road then it becomes a lot harder for them to get back because Trump has to fail and fail so bad that he pushes the population to the left fringe.  I concede he absolutely could fail to get things done, but it's hard for me to see a path where he pushes those in the center all the way to the left.

obama was neither far left nor a populist.

I don't know if I agree with that.  He ran on a very broad populist message of Hope and Change.  He appealed to a lot of people for a lot of reasons which is the definition of a populist.  He intentionally had very few specifics so people filled in the blank to believe he would do what they wanted. 

However, when he got into office he governed from the extreme far left.  I'm having a hard time thinking of a single far left thing he wasn't pushing for with all his power.
Marriage Equality and putting men in the women's bathrooms.
Illegal Immigration
Anti Gun
High Taxes
Government takeover of healthcare
anti-business
loved BLM and every other anti-white group
giving away billions (probably trillions) to foreign countries hostile to America in non-traceable cash payments (wtf) 
Big time abortion rights/womens rights advocate
anti-military (big time cuts)
hard core global warming propagandist

Those are just ones from the top of my head.  I know you're probably further left than he is on a lot of these issues, but that doesn't mean Obama isn't far left.  ;-) 

because the Democrats kick anyone out that isn't lock step in line.  I know people like to bag on the divisions in the RNC, but it's a lot more healthy to have strong debate and changes within a party rather than have out of touch whackados running the party and forcing everyone to march in lock step. 

No matter what, time will tell if they're doing the right thing or the wrong thing.  Based on the last poll I saw for the general election Trump would now win the popular vote by more than 3% and destroy Hillary even further.  In other words, people are liking what they're seeing out of Trump.

If he gets his 15% corp tax cut in, he will be unstoppable in 2020 because the economy will be roaring like a new Lamborghini.