The vvti 1jz never came in the supra, that alone makes the swap much more complicated. The ECU is different, the wiring is much different, the engine mounts are different. It also has slightly less in common with the 2jz, making parts harder to find.
The vvti swap has been done before a few times. If I remember correctly Kaizen motorsports (in the vendor section), has done it before.
IMHO the vvti swap is not worth it unless you have the extra time and money and want something a little different. If you intend on going for high hp, it will make your life harder simply because parts are hard to find if nothing else.