I've said this before but it's something I feel very strongly about so I'll say it again.
My users want to be able to customise what content they see and how they see it. They want to be able to ignore threads, ignore forums, ignore users, and decide how forum content is presented to them. Some like the most recent post in a thread to be the first post, others (most) want it last. They don't want to have me decide how they use the forum, they want that power. There is so much functionality and so many options missing in XF1's core - things that I consider basic stuff - that I am forced to use a dozen or so add-ons to try and achieve the kind of functionality my users want. All of the add-ons are developed independently so none of them work with each other without expensive custom coding, so it has never quite gotten to where my users would like it to be.
Developers aren't king, admins aren't king, forum users are king. Please create XF2 around allowing the users to decide for themselves how they want to interact with the community and give them the tools to do it. They are crying out for it.
The reason forums are on the decline is because they aren't giving users what they want. People want choice, they want options, they want to get value out of the community and they want to do it their way. That starts with the software. Make it fast, flexible, and load it with user options that let people feel at home, not like they have been invited to someone else's house and told to do things their way.
Choice, choice, choice and more choice.