There has been a lot of change in Activiti - even between versions 5 & 7. So for that reason, it's almost impossible to say how hard or smooth an upgrade from 2.0 will be - take a look at this thread re: upgrading from 5-7. I would approch this via incremental upgrades, and even then you may find that you have to modify models, etc, as you go.
Digital Community Manager, Alfresco Software. Problem solved? Click Accept as Solution!