A slide deck from Impact2013 said that WAS 8.5.5 is at servlet 3.0. The recent 8.5.5.next notes didn't mention anything about updating that.
This page from Oracle shows the certified servers:
http://www.oracle.com/technetwork/java/javaee/overview/compatibility-jsp-136984.html
If you care to look at any other servers, apart from glassfish the wildfly beta is reported to support servlet 3.1 (and Jave EE 7 in general) but I have no idea when to expect the release.