I found it funny how he said he wasn't going to spoil it but then let loose a pretty big spoiler for the new campaign lol. Sounds like they are trying to wright Relias as a tragic Hero that just can't do anything right. What's he going to do in the next expansion summon a new evil Titan? Got to hand it to him though the world would be a lot more boring without Relias. And here I was thinking this expansion would be him getting to redeem himself, and purify Ceresa so we could have a Druid character or something.
As for the mechanics changes they talked about i'm not really sure I like some of the stuff. First one that rubbed me wrong was the binary hero choice. So every so often two heroes show up, and your forced to pick one. Why? Why would you ever turn down the other guy? In FE now it's a financial thing if I have enough money to pay both I can hire both. So why remove that logic, and make it kind of a set in stone gamey mechanic? It also seems to take kind of a cool thing from the Betrayers ability to hire both Kingdom/Empire heroes. That said I do agree with the idea of making hero acquisition less of a luck of the draw map generation thing as that could get very unfair, and annoying.
Second kind of weird thing was the new way heroes level. So it's no longer picking random options but just a standard talent tree? Are the trees themselves random at all? Seems like it will get boring. Once again I agree with what your trying to do making it less luck based but I think some of the old system should carry over. Maybe make it like Fallout 3 where you can level towards being a fighter/mage or whatever but then also choose a random perk. With the perks just being minor things that add extra flavor like the Dragon Slayer perk or Man vs Fallen.
I'm looking forward to the new tactical battle elements though. Even if Axes sound really overpowered since Cleave was always the best. Line of Axemen sounds like an easy win. Especially if it still has backswing. Since I had come to grow to love that almost as much as Counterattack. I wonder if this means there will be zero mana abilities standard for Mage heroes now. In any case i'm glad they stepped back, and realized having the tactical side be boring just so Empire building would determine the win was not that fun. This is will probably be the biggest improvement to fun factor for the game to me.