From http://www.devexpress.com/issue=Q442195:

We recently allocated a part of our resources on testing the Workflow module under .NET 4.5 and it all worked fine. The module itself does not even need to be recompiled under .NET 4.5 explicitly, because the new runtime will be used automatically if your application is targeted to .NET 4.5. As for the new features introduced in WF 4.5, you can see what is available in the rehosted workflow designer from this article: Support for New Workflow Foundation 4.5 Features in the Rehosted Workflow Designer. We regret to inform you that Microsoft made not all the aforementioned features available in the workflow rehosted designer, and I am afraid we cannot do much on our side to overcome this. Feel free to contact Microsoft directly via their support forums if you require availability of the remaining features in the rehosted designer.