As of November 12, 2006 Ant 1.7 is now a Release Candidate.
Are you not keen on supporting 1.7 until it is finally released?
Oh c'mon, be reasonable, have you seen this list:
http://jira.jboss.com/jira/browse/JBSEAM?report=com.atlassian.jira.plugin.system.project:roadmap-panel
Right now Ant 1.7 support is the very least of my worries.