There's a right place and a wrong place for infinite scrolling, based on type of site/app, content, site traffic, purpose, etc. Even if two sites use the same tool, their purpose and audience may dictate what functions are needed or not. (Which is why infinite scrolling should be a preference setting, if it exists at all.) The ol' form fits function thing.
Davis why wouldn't you like infinite scrolling?
I'll bite. Options/preferences aside, a discussion board is not the right place for infinite scrolling, for the simple reason it's unnecessary. Let's consider the contexts of use...
What I interpreted from @Franz earlier is that the All Discussions page was the context for determining infinite scrolling in Flarum. But that's probably the one page people will do the least scrolling on. A normal routine for most (busy) people would be to land on the page, see what the latest discussions/updates are and dive into a specific thread. Nobody is going just keep scrolling and scrolling the All Discussions list of old, dead topics. Why would they? When somebody posts in a thread they follow, it rises to the top. No scrolling for it is needed.
But what about context for a single discussion? Tags? There will never be enough content in those views to remotely justify infinite scrolling. Most discussions peter out after a few replies. But let's say you have 50, which is well past the average even in big forums... you still don't need infinite scrolling for that. Infinite scrolling isn't solving anything in a discussions system because there's no single view with infinite content. Quite the opposite. So it's existence is counterproductive, IMO. Threads like this are not realistic; they're a false problem for a solution that's not needed.
I think the little scroll indicator at side of discussion threads (from "Original post" to "Now") is great. I love it. That's a useful and unique feature. I've never seen that before. It's also immediately obvious to users how it works, which is a boon for usability. And, frankly, it's all you need to provide. It does the job nicely without being annoying.