We have couple of workflows running on AEM Forms JEE. We are thinking of using the similar workflow in OSGi. To start with rendering a PDF form using a xdp. I created the workflow and given the payload through an absolute path where the xdp is located. When I started the workflow, all I got is a notification in inbox where only I could see the xdp as payload and option to complete/delegate the task etc.
I was interested to see if the PDF document comes as an output from the workflow as it used to be in osgi. Also, I could not find an option to make a variable as input or output, so that when the workflow gets invoked it would ask for an input variable and would show the output.
I have been a LiveCycle / JEE developer since the beginning of times. Honestly, AEM Workflow is no replacement for the orchestration engine in JEE. You can replace some aspects of render services etc and maybe some very basic interactive flows with users - but that is way more simplistic compared to the JEE engine. You cannot migrate a JEE solution with all its aspects to OSGi. If you start a fresh OSGi based system/project then you probably have completely different use-cases where the capabilities might match.
You can write your own services or extend the workflows with Java based custom steps - but that is more geek stuff than was required in JEE - still it is possible to integrate workflows in custom services and offer SOAP or watched folders for batch invocation. AEM workflows are not like orchestrations which become services with end-points automatically.