I believe that this is what they are aiming for (I hope) however it's not quite there yet. Perhaps this is the reason the update to V4 hasn't been pushed to the V3 users as of yet. Personally the Sandbox feature in V4 feels very much like a Beta to me.
Until the sandbox issue is solved I'd stick to using Sandboxie or Returnil.
I've got a copy of v3 & v4 and just reinstalled v3 back on this PC. v4 still seems to be a little to buggy.
I can run my malicious file test on the other computer with the VMWare. Tip; If your not very careful with Returnil it will cause blue screen events on Windows 7.