The ADT now contains a few more refactorings which can be applied either from the layout editor or from the layout XML editor.
First, there is "Change Widget Type":
In addition, if the current id of the widgets include the current widget type (such as a <Button> widget named "button1"), then the id will be changed to use the new widget type instead (e.g. "imageButton1") and all references updated.
We also have some metadata for which widgets are "related" to each other. So when you bring up the "Change Widget Type" dialog, if you are converting an AnalogClock it will list "DigitalClock" first, and so on.
The second new layout is "Wrap In":
This is using the Eclipse refactoring infrastructure, so you get previews of the edits to be performed:
Last, but definitely not least is the new "Change Layout" refactoring.
However, for some supported types, it attempts to preserve the layout. For example, it can do a pretty decent job converting a LinearLayout to a RelativeLayout.
Note also the "Flatten Hierarchy" checkbox in the dialog above. This is supported when the target type is a RelativeLayout. This will attempt to not just convert your selected layout, but the entire layout hierarchy under your select, and flatten it into a single target layout! It will skip layouts that have visible artifacts (such as a drawable attribute), and currently only flattens nested LinearLayouts, FrameLayouts and RelativeLayouts. It tries to take layout weights, gravity, order etc. into account.
NOTE - this is still a work in progress - but hopefully gives a useful start for some layouts.