Decided to test out a little more in depth:
Show History button is still greyed out after installing on another system. I tested by collaborating a test model, here are the steps I took:
1. Created new model
2. Saved locally (Show History button active)
3. Collaborate tab - Collaborate
4. Once collaborated, Show History button is greyed out)
5. Synch (added a comment)
6. Closed model and tried to access Show History button, pointed to the model but DO NOT see my comment
7. Under Collaborate tab - Manage Cloud Models, I am able to see the latest sync AND my comment.
Concluding this feature only works for locally saved model, not Collaborated model or there is a bug/error/setting in the steps above. Further concern, Show History only shows two syncs while Manage Cloud Models shows every sync including comments. In addition and perhaps because of this, Worksharing Monitor doesn't even see any models open or synching.