I think the idea of “let’s use BFS and Tracker for everything” usually does not work all that well when you try to use it for more than fun demos. Tracker does one thing well: file management. Trying to get it to do more things does not work.
This applies to email: at first, the idea of “all your emails are just files” sounds nice. But then you try to use it and find out that Tracker cannot easily do simple things such as showing your emails grouped by threads, in a tree view, seeing who replied to who. And that’s not the job of Tracker. And that’s why we got a more normal looking lail client, that’s Beam.
Caya is the result of a similar thinking starting from the IM Kit, I think. The initial idea sounded nice, but it didn’t work so well in practice. Your instant messaging rooms and contacts are not files, and Tracker isn’t a great place to manage them.
Now, for mails, it works somewhat fine. Beam still use the standard email format. It makes sense because emails have some data to store. But chat contacts? What would you put in the file? Just contact information? Offline conversation logs?
It is a work in progress and UI often look like that when work in progress.
I think one problem is having lots of margins everywhere, whereas in Haiku apps we are used to very compact layout, not wasting a single pixel. This is easily solved later on, and not something to spend so much time messing with right now. The importance of the UI at the moment is that it allows testing the features. Cleaning it up is not so difficult for someone who is used to doing it. A small margin here, a bit of bold text there, and suddenly it looks 1000x better.
Also this is nothing a sketchbook can fix. Sketchbooks are not good at discussing the size of pixel margins.