Yes, going to 2.6 is a wise decision, you will get Java 8. Anyway, in the git controller repo there is no STRAM mode, but it is quite simple change in the RuleEngine.java code. However, the official demo design with the home automation example uses the rule engine in the STREAM mode. You can take a look on it’s rule’s file and you will see syntax which is valid only in this mode. I don’t remember from which source this controller was build but I know that the demo itself is run on AWS and setup from the docker image available on hub.docker.com. Therefore, if you are working with docker (and if not you should 
then there is an easy way to get what you want.
Kind regards,
Michal