Some of the UAs (and now Xanathar's Guide) had material that felt like it would fit a specific Eberron niche, only made more generic. For example, the College of Whispers bard is a perfect fit for the house Phiarlan/Thuranni spy-bard, and the Circle of Dreaming druid is at least in theory a good fit for the Greensinger druid sect (although Greensinger magic is more about messing with people's minds, while Dreaming druids are more about healing).