For the long-form stuff I think this is fine. People get that these articles are "different". They assume they must go to some dedicated page to read them, so it's not actually causing much harm.

I think it's actually bad UX when one of these articles shows up in the normal microblogging feed.

But if we had just another note kind that showed up in some clients but not in others that would be interpreted as a bug on clients that don't show it.