I would really love to see multi-site support for Xenforo. I don't mind paying more for it, but I really would appreciate a built in option to support multiple sites from the same settings, users, plugins, etc. with easy navigation between the domains. Similar to WordPress multisite. There is a multi-site addon, but it is difficult to configure, and and is not compatible with most add-ons. I would like to be able to build a network of forums (for gaming).
Its great that there is an addon for this, but its extremely risky to be reliant upon a third party for such fundamental functionality. because multisite functionality needs to work with all addons and any update of XF and addons. If the multisite addon or support for other addons breaks then the webmaster has a serious problem.
It would be so much better to have this in the core and would undoubtedly lead to more license sales for XF.
Some benefits of this suggestion:
manage/update multiple sites from one back end
single sign on for users
reuse (some of) the same content to create new sites
This should be carefully thought through first. Sharing these informations between different sites brings a lot more trouble and things to consider than you might think.
To start of: What should happen if the 'main Installation' goes down for some reason? Will all other sites also become unavailable? Is this enabling you to indirectly DDOS multiple sites at once? And that's only the beginning of a long list.
You should be aware that this would be a rather huge project if you want it in a way that suites XenForo and modern standards and huge projects require a lot of time. Time that - in my opinion - is better invested in other features.