Proposals #1 and #3 are interesting, but I must vote against #2, personally. In my opinion, taking back moves greatly reduces the integrity of the game of chess. The reason I say this is because taking back moves is never allowed under any circumstances in OTB tournaments. Chess.com claims to be a great place to train for tournaments, but if chess players here were to become accustomed to taking back moves occasionally, they would be less effectively trained for real-world chess.
One of the aspects of chess that I love so much is that I make my decisions, and even when I need to make a critical or gutsy decision, I go for it! I'm committed! Sink or swim! 
Especially in Online Chess, the Submit button truly does remove any and all excuse for bad moves and places the responsibility thereof squarely on our shoulders. Depending on the mutually agreed-upon time control, we have anywhere from 24 to 336 hours to decide on a single move.
You said in your original post that you "agree [that these suggestions] aren't all good." Just out of curiosity, which idea(s) do you acknowledge as not good? I also wonder why you would suggest to Chess.com any proposal in whose efficacy you didn't even have confidence.
During my experience on chess.com, I grew to desire a few possible features, which in my oppinion would be a great addition to this site.
#1-Customizable board & pieces
I contribute to a spriting website, in which I design very small sprites for classic DOS projects. While drawing those sprites, I came to wonder "What if you could actually edit these chess pieces and the tiles?"
The website could have a "Chess editor" section under the "FUN" tab, in which you could do all those things under a template:
#2-,,CANCEL MY LAST MOVE" option
Let's face it. All of us made an accidental move once, either on live, either on online. Sure, the "SUBMIT" move button is very handy (I personally use it on online one) however, even with that, it can happen. The "CANCEL MY LAST MOVE" button would basicly cancel your last move IF BOTH PLAYERS VOTE.
Both players must agree. If you propose the cancellation of your last move, the player will see it on his screen, just like the draw proposition. From that screen on, he can either accept or reject. If the player has some common sence he will accept.
#3-Quote of the day
We have puzzles of the day, opening of the day, and more, but what about the quotes? Every chess genius left a quote on this earth, and quotes truly encourage players and show them the ways to mastery. I personally posted all amazing quotes on my notes, but having this suggestion would just be a general delight, and an improovement.
These are my suggestions. I hope some of them will be heard. While I agree they aren't all good, it's worth a try.
Comment on your oppinion and this suggestion.