Microsoft has revealed what it is doing with Wunderlist, it is replacing it with something they are calling Microsoft To-Do. Microsoft, Android, iPhone, and web apps are available today. 

I don't understand why Microsoft needs to replace Wunderlist, I guess they found it too difficult to integrate with Office 365. The preview version currently available is very limited, it just has a single to-do list and a My Day filter view of that list. The preview version does not work with Work and School versions of Office 365. 

Historically, To-Do list functionality has always been a gap for Microsoft. For example, the Outlook Android and iOS apps do not have a to-do list even though it exists in Outlook and Exchange. 

Even back to Windows Mobile and Pocket PC, while Microsoft provided a To-Do app it never worked with Exchange. The gap has been left to third party providers to fill. 

I will be watching to see how fast Microsoft adds functionality to this app and when it provides integration with Office 365.