About 2 years ago I wrote a blog post describing what I would like to see in Workflow vnext: http://geekswithblogs.net/JoshReuben/archive/2010/08/25/workflow-4.0---not-there-yet.aspx

At the time WF 4.0 was a little rough around the edges – the State Machine was on codeplex and people were simulating state machines with Flowcharts.

Last year I built a near- realtime machine management system using WF 4.0.1 – its managing the internal operations of this device: http://landanano.com/products/commercial

Well WF 4.5 has come a long way – many of my gripes have been addressed:

• C# expressions - no more VB 'AndAlso' clauses
• state machine awesomeness - can query current state
• many designer improvements - Document Outline is so much more succinct than Designer!
• Separate WCF Service Contract interfaces and ability to generate activities from contract operations
• ability to rehydrate to updated flow definitions via DynamicUpdateMap and WorkflowIdentity

you can read about the new features here: http://msdn.microsoft.com/en-us/library/hh305677(VS.110).aspx

2013 could be the year of Workflow evangelism for .NET, as it comes together as the DSL language. Eg on Azure it could be used to graphically orchestrate between WebRoles, WorkerRoles and AppFabric Queues and the ServiceBus – that would be grand.

Here’s a list of things I’d like to see in Workflow 5.0:

• Stronger Parallelism support for true multithreaded workflows . A Workflow executes on a single thread – wouldn’t it be great if we had the ability to model TPL DataFlow? Parallel is not really parallel, just allows AsyncCodeActivity.    
• support for recursion
• an ExpressionTree activity with an editor design surface
• a math activity pack
• return of application level protocol (3.51 WF services) – automatically expose a state machine as a WCF service with bookmark Receive activities generated from OperationContract automatically placed in state transition triggers.
• A new HTML5 ActivityDesigner control – support with different CSS3  skinnable hooks,  remote connectivity (had to roll my own)
• A data flow view – crucial to understanding the big picture
• Ability to refactor a Sequence to custom activity in a separate .xaml file – like Expression Blend does for UserControl
• state machine global error handling - if all states goto an error state, you quickly get visual spagetti. Now you could nest a state machine, but what if you want an application level protocol whereby each state exposes certain WCF ops.
• DSL RAD editing - Make the Document Outline into a DSL editor for adding activities  – For WF to really succeed as a higher level of abstraction, It needs to be more productive than raw coding - drag & drop on the designer is currently too slow compared to just typing code.
• Extensible Wizard API - for pluggable WF editor experience
• other execution models beyond Sequence, Flowchart & StateMachine: SSIS, Behavior Trees,  Wolfram Model tool – surprise us!
• improvements to Designer debugging API - SourceLocation is tied to XAML file line number and char position, and ModelService access seems convoluted - why not leverage WPF LogicalTreeHelper / VisualTreeHelper ?

Workflow Team , keep on rocking!