Will rock, or even rock-influenced pop, return to the mainstream in the Roaring 20s?

I sure as hell hope not, you deserve nothing. Mainstream is there for those that suck at finding their own way in the internet age.

https://www.youtube.com/watch?v=kfh1f4fD0_c

https://www.youtube.com/watch?v=czxXjEBqcQg

I doubt it.  Rock music's popularity is gradually declining as its audience ages out.  There may still be the occasional rock hit but it's becoming a niche market, the way jazz did in the 1960s and 1970s.  

Country is becoming more mainstream. I see rock country as one of the styles that is on the rise.

I also see the desire for the return to rock as similar to a desire in the 60's for a return to Western Swing.

The division of music into Rock/Pop/Coutry/Hip-Hop/... that might have been appropriate in the past is not longer a valid division. Everybody is drawing from influences from everywhere. And the result doesn't fit into those boxes. 

Rock from the '60 and '70 has influenced everything. But it isn't the '60s or the  '70s, and that kind of music isn't gonna be as big as it was. 

Instead of looking to the past to define current music (and/or evaluate current music in reference to that music), one should look to the past to find where current music came from and to evaluate current music on its own terms in relation to other current music and in relation to ones ears and ones tapping toes.

Yes, rock will be a big influence on mainstream music of the 2020's. 

No, purists won't call mainstream 2020 music rock.

Not likely. The key element to the best in rock was allowing the artists to create what they wanted to create.

But, these days, the music companies want to control everything in the production chain, so as to make the most money for themselves while starving the actual artists.

Read the linked article and note that despite it's headline, pretty much nothing it speaks of is actually rock music.

probably  not, but anything's possible

it just depends on what people with actual talent decide to get into, and what audiences decide they want to respond to.  no predicting any of that.