To cut things short. In previous versions of GXT you created your model classes by inheriting BaseModel or BaseModelData. Sencha however have left this approach, rendering old model code useless.
To easily convert all code in one go I created this little python program, and ran it on my code: https://github.com/rohdef/GxtModelConverter
Apart from that, porting my model and my server code seems pretty painless. The GUI code on the other hand is probably going to be a different story. There have been a lot of changes, and I’m looking forward to all the improvements and the final version