The text mesh doesn't feed back to the size at the moment. If you would like to implement this yourself, I suggest
1. Create a layout object and attach to the textmesh. Whenever the text changes, change the layout size to match.
2. When you add this layout to the parent layout, use AddLayout( item, tk2dUILayoutItem.FixedSizeLayoutItem() )
3. If added in the correct order, everything should be sized correctly in your main layout.
The remaining issue is handling resizing text. To cope with that, change the text size, change the text meshes layout size (SetBounds). Call DoChildLayout on the parent layouts moving up the hierarchy for everything to work properly. All of this was planned but we haven't had the time to implement it properly. It is likely to be in a future version.