I think that with Tri, Bandai is going all out with the best things Digimon ever had. So, let me explain:
We have the beloved Adventure kids. They have grown up and are the ''main'' cast as far as we've seen. Adventure 02 in general seems not to get much praise from the fans because of certain ways that season rolled out. How Daemon was ditched out or how the character development wasn't as good as 01, everyone who doesn't like 02 has a different reason. (I personally do not dislike 02, I grew up with it as much as 01 so I like both, though I prefer 01 of course).
Now, Bandai might think: ''Well, Adventure 01 and 02 are played in the same universe. If we make a coherent and interesting story with Tri, we can sort of ''fix'' the image that 02 has if we make a good trilogy that connects everything.''
That's because 01, 02 and Tri are pretty much a trilogy. We have the 01 arc, we have the 02 arc and Tri, they might go in a sort of way that enlightens us on certain things about 02 (How Daemon fit into the narrative and how we came into play, the whole Dark Ocean idea and whatever else they might plan).
Now, from what we've seen of Tri so far, with the first 4 episodes and with the trailer to Determination. Something happened to the 02 kids and to the Digital World itself. Wait, the Digital World? How so, how do you know that? Because of Alphamon. Alphamon is a big clue as to what may be going on.
Alphamon shows up when the Digital World is in a crisis. We've seen digimon infected as well (Remember 02? We'll get back to that). Now, Alphamon was apparently after Meikoomon, for some reason I do not know. Maybe she is immune to the infection? Maybe she is what caused it? We'll learn later on.
Now, in 02 we were shown Ryo belonging to Ken's backstory and how Milleniummon infected him, thus giving birth to the Digimon Kaiser.
What I think is the ''main'' story of Tri and the whole adventure arc is involving Ryo and Ken as what made everything happen. Milleniummon was somehow born after Machinedramon was defeated, a while after Apocalymon was defeated, how so I do not know. Ryo and his partner Monodramon defeated Milleniummon but not before Milleniummon planted a dark spore into Ken.
Years later, Ken grows up to become the Digimon Kaiser. What does he do later on? He creates Kimeramon. What if that was Milleniummon's main goal? To have a child grow up with such ideals that it would create Kimeramon.
Now. some people say Milleniummon was born from Machinedramon and Kimeramon's drifting data bring combined but what if Milleniummon was technically born from Machinedramon's data and other digimon? What if Kimeramon did not fuse with Machinedramon but Kimeramon gave birth to a new Milleniummon?
So Kimeramon dies in 02. His data lingering around giving birth to a Milleniummon later on. So now we have a new Milleniummon, who might have revived Myotismon and have sent Daemon to the real world, explaining how they both came to be.
We've arrived on Tri. Milleniummon has evolved into something greater. Inbetween 02 and Tri, Milleniummon became ZeedMilleniummon, bringing a disruption to the Digital World. So, something happened and he has infected the Digital World with the same spores Milleniummon infected Ken before 02. This brought a huge crisis to the Digital World, hence Alphamon appears. Now, for ZeedMilleniummon to have infected the Digital World, he needed someone to do that for him. But he did not want to rely on Digimon, like Daemon and Myotismon failed but in this case, he relies on children like Milleniummon did. Hence, the 02 kids are abducted and turned into slaves of Zeed, spreading the infection with the spores.
I think Tri will be this: Alphamon is not the antagonist at all, he is just acting in the Digital World's best interest. ZeedMilleniummon is behind it all, using the 02 kids as a means of spreading the spores and infecting Digimon and since we've seen Imperialdramon being ''infected'', it's safe to say that either Daisuke or Ken are the Kaiser, or they both are along with the rest of the 02 kids (with the exception of Kari and T.K).
TL:DR~ 02 kids are pawns to ZeedMilleniummon, Alphamon is a good~ish guy, the infection are the spores from 02 doing their work and Meikoomon is perhaps the key to save the Digital World.
Sorry for my rambling!