Emoji reactions to comments are good, but I miss one: the 
or 
checkmark, to mark something as done.
Now I have to reply in a thread that something is done, but if a thread contains several topics, it becomes complicated.
I tried to use the 
plus or the 
thumbs-up instead, but they have a slightly different meaning: plus means «+1» and thumbs-up means «I like the idea».