It isn't change for change's sake, it's a known problem seeking a solution.
I like the midline invasion addition. Chess is basically a game of war, and in war you don't have to kill the king to win, you simply need to conquer enough land. With the midline invasion, the king is no longer a piece to be protected, he can go on the offensive, march his army forward, and take over his enemies land: a much more dynamic game.
And losing if you have no legal moves is a major improvement; it never made sense the other way, if I can move and you can't why is it a draw? That's one change that shouldn't get any complaints, except from people who like to turn losses into stalemates by forcing themselves into illegal moves; I've seen someone play that way, it was annoying. These are two very simple changes that add a lot more engagement to the end game.
I'm going to need to think about the armies and duelling: these are two major changes that don't just add some addition strategies to the end game, they completely change everything. That could be good or bad, I'd have to play a few games to decide. The duelling mechanic adds a bit of a bluffing to the game like poker and I don't like that. In chess, if you're winning there's no harm in letting that show, and if you're losing it's acceptable to look a little worried. Now you have to be careful not to tip your hand (to use a poker term) and give away that you know you're going to win or lose a particular duel: there's the potential for a game to be won or lost based on how "certain" your opponent looks when duelling, either so you know to throw a large number of stones or to abandon the attempt and save them for later. I do not like that, I cannot bluff, and I suspect a lot of current chess players can't either. You watch the masters, when one of them starts losing they start sweating. Duelling is not just an addition to the game mechanics, it adds a new requirement to the players, one that will be met with resistance.
The additional armies are a lot to take in, and I'm worried that without very careful balancing and a lot of plays it's going to emerge that one army is preferred almost exclusively, and then you're back to the same boring left-right symmetry they were trying to avoid. A board game is not an MMO, you can't just update everyone's rules at once so we're all playing the same. Some people play chess occasionally and won't bother keeping up with any rule changes, and it is very unfair to expect them to compete in any way, even casually, against someone who knows that rooks can do that thing now, or that knights are no longer allowed to do that other thing, or whatever. For this reason it is very important that if armies are introduced that they are properly balanced from the start and not be subject to periodic nerfing as we see in online games.
Personally I think they need to bring back the
Mega Chessatron.
I would be quite fine with the changed win conditions, and I'd even still gladly call that chess; I may even start proposing it now in the rare occasions that I play. The duelling system adds something that I'm not at all comfortable with and I don't think they've thought that through: I'm aware that I'm not good enough to play professionally but I know that with enough (a lot of) practice the potential is at least there for me to compete. If they add duelling it doesn't matter how much practice I get, I will be outbluffed in duels and will lose a lot of stones and pieces that someone with more emotional control wouldn't. Finally, the addition of the armies doesn't just change the game, it effectively makes it an entirely new game: I don't think it should carry the moniker "chess", it is an entirely new game in its own right based on the rules of chess and should be given an entirely new name.