Judging as an adult, the stakes were higher in KK2, but for some reason Mike Barnes scared me more as a child. I had nightmares about him as recently as the first Karate Kid DVD box set release (old enough to not be scared of fictional karate bad boys).
That said, Johnny, Chozen, and Barnes were all teens during their storylines. They had a whole 30 years of life to grow into better or shittier people. I give props to the writers for writing believable arcs for Johnny and Chozen. While I would love them to gimmick another redemption story for Mike Barnes, it would be nearly unbelievable to have a hat trick.
I'm totally on board with Kreese and Silver remaining shit bags through out the last 40 years. We had an entire movie where Sato went from villain to sympathetic. It was done so well, I wish the film was longer to let good guy Sato get more screen time. But his villainy was still rooted in an honor system that no one challenged him on until shit really hit the fan. No one held him accountable because they feared him, but once he realized how fucked up he had been living, he changed. I don't see Kreese or Silver going that route.
Any redemption from those two would have too many strings attached. Kreese would only take out Silver now out of spite and revenge. Any alliance he'd form with Eagle Fang or Miyagi-do would be a brief marriage of convenience. I believe he would immediately turn right back into an antagonist if he got even with Silver.
I feel the same way about bringing Barnes in. I don't know what his story will be, and I'm sure it'll be written well. But armchair quarterbacking, I see him coming in bitter and self serving. Like my fan fic above about Kreese, anything he does with other characters will have strings attached. An alliance with Silver will be to get even with Daniel and then he'll swiftly turn on Silver. An alliance with Miyagi-do will be the same. An alliance with Johnny will just result in a season of Daniel Larusso whining about "watch out for that guy, he's dirty, I'm telling you, back in the 80s he was mean to me and my friends!" Since Johnny and Miguel are on a trip in a side plot to find Robbie for an undetermined amount of episodes, I don't know that this hypothetical plotline would have time to breathe. And there will be not enough time for Barnes to just show up to fuck with everyone as a solo act (with or without his own dojo behind him). Every main character, save for Johnny, should be on Mike's shit list. And if Barnes and Johnny interact, I predict Barnes being dismissive of him at the most pleasant end, and completely deriding him until they come to blows at the least pleasant end.
Can't wait.