I think the trailer is just going to be fluff gameplay footage to hype the season, no huge new announcement. If the hero changes are something more than numbers, they’ll reveal those. It’s possible they could add something else, but we know it’s not a hero, a map, or major progression changes. Dunno what else there is that would be exciting.
The “content roadmap” is weird. I can only guess that it’s talking about shop skins and the winter event. But it’s a strange way to phrase that. Can’t really think of anything that I would expect to be rolled out partway through the season.
I do expect a holiday event date but not a full reveal. Perhaps there will be a mini event or something planned for January. There’s also the mid season balance patch which could get a date. Even all that feels light to be releasing a “content roadmap” though. The very idea of the seasonal model they told us about was that everything is added on day one of the season. I wonder if they’re changing that somehow.