The error said that the feature activation timed out after 20000 milliseconds. (sorry, bit vague I know but to busy fixing the problem to cut-n-paste it before finding the solution)
Looking at the Event Logs hinted at a service bus issue:
Failed Service Bus Operation: System.OperationCanceledException: 40400: Endpoint not found.
I tried the usual (re)Register-SPWorkflowService but that had no effect. I tried restarting the Workflow and Service Bus Services aswell as the Server, but to no avail.
The only way I was able to solve the issue was to leave and then re-join the Farm.
To do this run Workflow Manager Configuration and click "Leave Workflow Manager Farm". Follow the prompts.
Run Workflow Manager Configuration a second time and select the third option Join a Farm. Enter your details and follow the Prompts.
After the configuration was finished I re-ran the powershell registration command:
Register-SPWorkflowService –SPSite http://devintranet.domain.local –WorkflowHostUri http://server.domain.local:12291 -force -ScopeName Development –AllowOAuthHttp
I was then able to successfully deploy my projects that contain workflows.