I would like to see added support for KVM hypervisor (see ticket 4149427) on virtual appliances. This would require support for additional block storage device types, specifically virtio drivers.

I was able (after messing with the install ISO's /etc/fstab entries) to get it to install and it's working great!

Could NOT import hyper-v nor vmware appliances due to the block device type.

Import pre-configured appliance
Configure block device as VirtIO, and NIC as Intel E1000
Insert FreeBSD installation DVD into available CDROM
Set Boot Order such that the CDROM is booted first
After the VM boots to a prompt asking if you want to continue to "Install" "Shell" or "Live", select "Shell"
Run the following commands:
-> mount /dev/vtbd0p3 /mnt
-> vi /mnt/etc/fstab
(replace all occurrences of 'da0p' with 'vtbd0p' - a sed command would also likely be viable)
-> umount /mnt
-> poweroff
Set Boot Order to boot from the block device first
Eject FreeBSD ISO
Boot VM

I would be very happy to work with development to add this.