There is a new post about the new features of ISA Server 2006 SP1 in the ISA Server Team blog. One of these upcoming features will be the SAN Certificates support.
This Service Pack introduces new features and improved functionality for ISA Server 2006 Enterprise and Standard Editions. The new features focus primarily on enhanced troubleshooting mechanisms designed to help you identify and resolve ISA Server configuration issues. Also included in this package are the updates we've promised for so long, such as SAN certificate support.