The spring features should all be named spring, and use version ranges to differentiate between the various spring version supported.
Currently Spring 3.1 is named spring31, and not spring. This causes problem for end users, such as installing both spring 3.0 and 3.1, when they only want spring 3.1 etc.
See more details in that nabble link.
The ciritical issue is that SMX / Camel etc cannot reuse the spring features of Karaf when spring 3.1 is the new default choice.