I would really like to be able to reply to a message, I think this will be really useful in groups, but I think replying to a message is actually a subset of the quoting functionality!!! where replying to a messages is full quoting the message, but quoting is more flexible since you can partially quote a message, so you can reply to a specific part of the message.
Related to this: Requests from my girlfriend)
and I don’t think that being able to reply/quote will make useless: [Discussion] Make DC a replacement for MUAs?