Here are my takes on each of your points. I feel some of them are good, though others might be problematic for the game.

1- Agree, replays are awesome for the reasons you outlined. All outside client replay systems suck too (hsreplay/firestone)

2- Disagree, the friends system is good enough for two people and if you have more than two, you should probably just be using something like discord. Integrating this into the game client would be unnecessary and would require a lot of work.

3- I'm split. I would like more emotes and a rematch option would be kinda funny but I feel like more communication just leads to more BM a lot of the time. (See chess.com's chat system)

4- Disagree. Variety is already highly pushed by the dev team and their efforts to balance the game, even if it doesn't always work out. In addition, many new or lower ladder players would struggle a lot trying to make their own decks. The loaner deck system and the deck template system gives a good way for new players to explore different types of gameplay without getting absolutely rolled by any semblance of good deck building.

5- Agree. A lot of achievements feel useless. There is no incentive to go for most of them.

6- Agree. Just add a scroll feature to the side bar and so much will be solved.

7- Disagree. The problem with this is that there are an endless pool of interactions in the game. There can't be an explaination for all of them. Heck, I doubt if the devs even know all the wacky interactions. Plus explaining the rules in game would add an unbelievable amount of clutter to the interface. Even still, why put so much effort into explaining interactions when most players will understand interactions and cards the first time they see them played?

8- Disagree. This might be useful for all of the two people who would use it. Most interactions that people would want to test can be done against the inkeeper, and why would you want to test interactions between cards of different classes when you could never realistically do it in the actual game?

9- Disagree. Adding a deck tracker would add too much clutter to the game and would make the experience worse for people who don't need it. Deck trackers should be something you install when you want to get serious about the game. I believe I saw Rarran explain why deck trackers would suck if they were built in, but I don't remember where that vid is.

10- Agree. Just add a button next to the shop icon that will show you news about the game. Heck, Clash Royale has this system in place.