We are using Drools in a Java 11 Web application via the kie-spring library.
This library depends on xstream.
The compatibility of xstream with newer Java versions is uncertain as described in this Issue which is already 3 years old and not going to be "fixed" as far as I understand it.
Is there a plan to switch to a different underlying technology or any other changes that would move away from xstream? Or at least a way to get rid of the JVM warning and assurance that it will work with future versions?
This is an XStream problem. The very link which is shared in the original question, provide some valid solutions to avoid the mentioned XStream issue.
Is there [...] at least a way to get rid of the JVM warning and assurance that it will work with future versions?
As can be seen on this change https://github.com/kiegroup/drools/pull/2988#issuecomment-658079653 modifications are already underway to resolve the mentioned issue as it manifests inside the Drools project which make use of the XStream library.
So this is resolved currently for the Drools' DMN module, and Kogito; if you spotted a specific module of Drools which is not yet updated, you are encouraged to raise a JIRA.
Question on StackOverflow is one of the channel we monitor as @schrobe correctly commented here; if you need a more back/forth exchange you can also interact with Drools developers via chat or forum. All these are valid channel that we monitor as originally described in the project get help page.
I hope this fully answers your original question, let us know if you noticed the issue in other modules!