Solaris 11Express, IPF and zones

I was disappointed to see that Solaris 11Express is still stuck on IPF 
4.19.

Any idea when the 5.x code tree will make it into Solaris?

I currently have a configuration where there are 2 Solaris machines.  A 
small server acting as an external NAT, FW, DNS, server, etc, and a 
larger internal server for typical internal services.

In the interests of saving upgrade costs and electricity, we'd like to 
move the external server into a zone.  Give it a dedicated IP stack and 
NIC to the Internet, create a VNIC/VNET between the external zone and 
the internal global, and then finally a NIC to the internal net.

Is 4.19 upto the task of doing this?  We'd be running IPF on the zone to 
FW the external NIC and provide NAT services, and again on the global 
zone to FW the global zone from the external facing zone.

Any thoughts or comments?