The WF Team has decided to deprecate the following WF3 types with the lastest release of WF4.5:
At this point it will not affect workflows built using WF3 other than a build warning that is encountered saying, "Warning BC40000: TYPE is obsolete: 'WF 3 types are deprecated. Please use WF 4 instead'". The WF Team is saying that the types will eventually be removed (post-.Net 4.5), so this is a great indication to start converting those WF3.x workflows... If you need help you can always ping me:)
Since there is not a replacement in WF4.x for System.Workflow.Activities.Rules or the rules engine, they are not being deprecated, however there are other alternatives for building rules within WF4.x using the workflows themselves. The WF Team's official post about the deprecation can be found here.