Have there been any safeguards or special rule changes within the DNC to prevent an unfair primary process as with what happened to Bernie Sanders in the 2016 election cycle?
First of all I will address claims that the 2016 Democratic Primaries were rigged. Tom Perez, Chairman of the Democratic National Committee stated as such "“We heard loudly and clearly yesterday from Bernie supporters that the process was rigged, and it was. And you’ve got to be honest about it. That’s why we need a chair who is transparent.” Tom Perez was not alone in making this statement, Donna Brazile, Interim Chairperson for the Democratic National Committee and Democratic senator Elizabeth Warren also stated that the primaries were rigged. Before we address what has been fixed for the 2020 primaries, we need to address the specifics of how the 2016 elections were "rigged".
The aforementioned Donna Brazile was also fired from CNN for leaking debate questions to Clinton.
All three later retracted their statements. You can take that as evidence that their statements were incorrect, and thus should be disregarded. Or you could fairly conclude that all three came under pressure from the DNC and Clinton faction to retract their statements. None of us will ever know, so it's pure speculation. Given that, we should not so blithely dismiss either of the possibilities.
What has been fixed for 2020?
Superdelegates no longer get to cast their votes on the first ballot. Hopefully that means that the media won't count their votes and call it an early lead for their choice (Kamala Harris most likely) in order to convince Sanders voters that there's no point in voting.
Apart from that, the party can still work behind the scenes to suppress debates, can still leak debate questions to the media, and still put their thumb on the scale in a myriad of ways.
To inject a little bit of personal opinion at the end here, the media is a far bigger issue than the DNC this time around. "Too old", "too white", "sexist", "Bernie bros", "spoiler", "communist", "unrealistic policies", misrepresenting the cost of his policies vs current policies, claiming he has no support among black and minority communities or women... We can expect the media to push against Sanders in all these ways. I don't think the DNC will play as big a role this time.
Note: The earlier version of the question when I answered specifically accused the DNC of being "rigged." I'm not really interested in playing chase-the-goalpost (the OP has an agenda). The current revision also still tries to indirectly suggest the process was somehow rigged, so it's mostly still relevant anyhow.
The idea that the DNC somehow rigged the primary to throw the win to Hillary Clinton is a myth not well-supported by evidence.
What really happened to Bernie Sander's campaign is that he was soundly defeated in the votes all along, not matter how you count them. That includes removing the superdelegate votes that one popular version of the myth claims made a difference. Additionally, the power the superdelegates had is often overstated, as they only offered about 15% of the total possible votes (versus the number needed to secure a nomination) and more than 15% of them actually did choose to vote for Bernie (not all coordinated in some conspiracy). Furthermore, Bernie's race always was a longshot, seeing as how he was an independent running in the Democratic party's race.
While it wouldn't have saved Bernie's previous campaign, in August of 2018 the DNC did drastically reduce the influence superdelegates have.
Under the new plan, which was agreed to on Saturday afternoon in Chicago at the Democratic National Committee’s annual summer meetings, superdelegates retain their power to back any candidate regardless of how the public votes. They will now be largely barred, however, from participating in the first ballot of the presidential nominating process at the party’s convention — drastically diluting their power.
Superdelegates will be able to cast substantive votes only in extraordinary cases like contested conventions, in which the nomination process is extended through multiple ballots until one candidate prevails.
According to the Wikipedia article you linked, the impartial private commentary some people made and possible suggestions of efforts to choose one candidate over the other came late in the campaign (important context that was often missing when news outlets discussed the documents Russia stole when they hacked the DNC servers), when it would have taken a massive shift in the voting to save his campaign (something he seemed aware of in interviews at the time, though he still continued the campaign). In other words, it actually would have taken some major rigging in Bernie's favor to really tip the scale by that point.
Additionally, the interim chair of the DNC following the 2016 primary, Donna Brazile, who initially seemed to buy into the myth, later concluded that she "found no evidence, none whatsoever" to support a rigged primary.
In case you were wondering, the "rigged DNC primary" narrative is one of many idea that Russia pushed on social media, and there are many such examples in this limited dataset NBC News published (a quick and probably incomplete dump of some examples based on some keywords, for those unfamiliar with CSV files). Of course, some less-reputable news outlets with an agenda also pushed this narrative.
So we're going to have to call this, Myth Busted.
Some poor rebuttals from the comments:
But Bernie's polls improved somewhat later on when he gained more name recognition. If they had scheduled things differently, Bernie might have done better.
In other words, if they had changed the way they do things and designed the game specifically to advantage a newcomer like Bernie, sure maybe he could have done a little better (that's all speculation). Gosh though, changing how things work like that for Bernie's advantage sounds like a rigged system, doesn't it? Plus, nobody in the DNC is psychic to really be able to plan any of this.
But I don't think the rules were fair!
You can argue all day about how you wish the rules were different to advantage whichever candidate you want, but the rules were the same for all players and they all agreed to play by them.
Not a single mention of the DNC hack
Yeah, because that would be a non sequitur. Just because something got hacked doesn't make it rigged. I do actually briefly reiterate the supposed evidence from Russia's hack as being dispelled by the Wikipedia article the OP linked though, there's really no reason to reiterate it all here, just follow the link if interested. Ironically, this is actually a positive review, even if the commenter doesn't understand why.
But Senator Elizabeth Warren voted for Hillary over Bernie, even though I think her ideals are more like Bernie's.
Someone voting for who they think will win the general election is hardly evidence of rigging. By that measure, all primaries are rigged. Plus, is it really that surprising a member of the Democratic party would vote for another member of their party over an independent like Bernie?
I assume the "unfair" process you are referring to largely refers to superdelegates who are not bound by any primary votes, as they voted overwhelmingly for Hillary Clinton.
For the 2020 primary, they are changing the rules so that superdelegates do not have a vote on the first ballot at the convention. Thus, if any candidate is able to get a majority of the pledged delegates, that candidate will win the party nomination.
Only in the event that no candidate gets a majority of the pledged delegates, will superdelegates begin to vote in subsequent ballots to decide the winner.
(Source: The Green Papers)