The first half of your proposal already exists: the single-player campaign. The second half of your proposal also already exists: the triumph leaderboards.
This is the exact question and answer from cs:
ME: Hi! If I post a friendly challenge for my warbase to my alliance chat, will my war museum affect it or my main museum? If I currently have coalitions active will they affect it?
CS: Thank you for reaching out to us. We would like to inform you...
That's true for how it's supposed to work normally. However in the bug you're referring to, it'll disappear if any ally responds to your request when you're offline. That particular assist will work, then the request will disappear from chat.
That was much better lol. I'm not here to criticize you, I'm just saying if you want people to identify and agree with what you're saying you should make it easy to read.