In no particular order:
1. Recycle integration, this will allow for proper audio quantisation within Reason, which would be particularly useful for vocals/guitar parts etc.
2. Add ability to move multiple mixer sliders at once and perhaps to add the ability to 'link' mixer channels together so that any changes made to one channel are mirrored by the 'linked' channel.
3. Change the way you have to manually type in your details each time you start reason to use REs, at the very least add a 'Remember Me' tick box.
4. Implement a less clumsy method of creating SSL mixer groups, perhaps by adding audio destination options to the programmer section of the mix channels in the rack, in a similar manner to Kong's drum output option for example.
5. Finally, allow for Reason to be a ReWire host.
Hope everyone agrees!