I want to have a workspace with 6.1.x and 6.0.x, it would be good to support that. Look here:
The problem is that Liferay Portal Runtimes for 6.1 assume Tomcat 7, but it is possible for it to target Tomcat 6. Also, it is possible that Liferay 6.0.x runtimes can target Tomcat 7. The runtime/server adapters should relax the requirement for tomcat6/7 if possible.