Done in hrev48354.
It was decided to do it this way because migrating from alpha4 to beta1 is not supported, and we don't want to have support for the old format in the notification preflet (it removes a lot of code to use the new format).
In some circumstances (eg if text doesn't contains spaces) I have noticed that the text inside a notification window, could go out of the screen, resulting truncated.
See the attached screenshot.
I was attempting to change settings for Notifications (I'd wish to change the Window width), once i click on "Apply" button, an alert window told me "An error occurred saving the preferences. It's possible you are running out of disk space."
Obviously I'm not running out of disk space :-)
hrev48327 screenshot attached.
Fixed in hrev48350.
DiskProbe was rewritten to use the layout kit, and this seems to work properly now.
Note that the font size is picked so that the horizontal scrollbar is disabled only (so a line fits the window as nicely as possible). The vertical scrollbar is not taken into account, as in most cases this would lead to a too small font (the header view minimal size ensures the window is always wide enough).
Fixed in hrev48348.