For me Sketchup PRO really has to earn its title. That isn't with rendering as there are more than enough capable rendering packages out there that integrate very well with Sketchup. My votes would be for:
-Hi poly modelling and faster handling of large models is the number one priority.
-Related to this is the ability to handle large models when it comes to actions such as exporting 2d DWG files, HLR pdf's and draping on to terrain. I've had many instances lately with large files I work with where it wasn't possible as it crashed. This has to be addressed for a pro application.
-Again related to above, the ability to use multi-threading and 64 Bit. This would enable the harnessing of already available technology to improve the handling of large models.
-Support for line weights and hatches
-Rock solid stability. It is much improved and rarely crashes but it could still be improved.
-Some parametric features such as roofs, doors, windows etc. Whilst it is easy to build a model, changing it is another story. If I decide that I actually want a 45deg roof rather than 35 I have to redo the whole roof. If I could just type in 35 deg and it instantly updates it would be a huge timesaver. The only problem is that Sketchup isn't Revit and it then starts to move away from its main idea. Some kind of add on would be worth considering however.
-Enhanced terrain tools particularly for reshaping such as a road tool
-Importation of Google Earth snapshots in colour
-Additional modelling tools may be beneficial for many but it mustn't be at the expense of the sketchup ethos of simplicity. If it was implemented it should be like the sandbox tools where it is a separate tool collection that has to be activated.
-The fat face tool sounds very useful too
As for Layout there was lots of speculation before it came out that it would be an easy to use CAD package with titles like 'draftup' being thrown around. I think there is a huge market for this and Google may do well to move Layout in that direction. I'd certainly use it as I still haven't found a CAD package I like and tend to do everything in Sketchup.
Kenny