I've been puzzled by this for a while. It's now pretty clear that BizTalk Human Workflow Services (HWS) is a dead-end. Additionally it seems highly likely that Microsoft will buy SourceCode and their product K2.NET. After all, SourceCode moved from South Africa to Redmond; say no more.
Microsoft CRM has its own workflow engine out of the box, but robust possibilities for integration with other workflow tools with only "SOAP-callable" APIs.
My guess is that K2.NET will be fronted as the "new" HWS and will be tightly integrated with Sharepoint and the Office Servers (if that's what they're gonna do), and possibly MSCRM. Windows Orchestration Engine (WinOE) will eventually be the core driver and the foundation for BTS, but also directly or indirectly consumed by other server products.
This aligns with current MS strategy for bundeling server products with OS functionality, just like they do with using Windows Sharepoint Services as a frontend for BTS and MS Project solutions.
The consequences of this is that we'll need to carefully consider where we build current workflow solutions. Building value into one of the engines that will not be continued is not desireable.
Anyways, I'm just guessing..