Hm. Perhaps I can't disassociate what represents mainstream media outlets from those that aren't mainstream, but I've detected quite a bit of enthusiasm from the establishment for AOC. I mean, you can imagine that the aftermath of 2016 could've played out very differently: you could imagine that instead of Democratic politicians with presidential ambitions largely embracing Bernie Sanders' political agenda, that they could've instead continued to try to galvanize support based on a need to confront Russia for hacking the election, punishing Facebook for disseminating fake news, and the whole host of other ways that centrist Democrats have tried to justify HRC's loss in 2016 (sounds terrifying!). But they didn't: they've embraced Sanders' signature proposals, and have competed with him by introducing some of their own, in effect trying to prevent getting outflanked by him from the left. It seems like, rather than being scared of AOC and Bernie, Dems are trying to harness the excitement around them, and have moved the party to the left (or at least the part of it that is running for president).
And since the 2018 election, the media has largely promoted candidates who are further to the left, despite the fact that the Democrats actually won its 2018 landslide on a much more moderate message than one might have expected given the political climate (most importantly, defending Obamacare), and many of the representatives elected are actually much more moderate than is generally depicted, especially in light of the skewed view that the media's focus on AOC, Ilhan Omar, etc, gives. So with the media in addition to the party, I mostly see enthusiasm, with occasional complaints when AOC says something that's factually incorrect.