Not without a fair bit of hacking, at least. Support for VirtualBox (i.e., the VirtualBox jail template, or some other point-and-click way to get VirtualBox running) will not be returning, but it may be possible to hack together a working VirtualBox jail anyway. I think there's some discussion of that in other threads here, but it's probably best to take the opportunity to migrate your VMs to a different host (either VB on a different machine, or bhyve on FreeNAS, or some other hypervisor on a different machine).