I think the deal is still being negotiated as we speak. But the good response of the third opus and maybe a bit of pressure from his entourage can motivate him to do this one (more than ever now that his baby, THE EAGLE PATH, doesn't seem to be convincing enough to be well received).
EDIT: message from John Hyams to one of the VD forum admins
It looks like US4 is going to happen. I'm writing the script right now, so I'm not going to release any details at all about it. What I can say is that it will be quite different from any of the previous films. I feel like this is a great opportunity, since I'm involved from the inception this time, to take my ideas even further than I did before. I'm excited about exploring these new directions, as are the producers.
Knowing the man can do and listening to him on the audio commentary, I'm definitely confident about this, so even though we could have done without a new UNISOL movie again, I know that with Hyams on board it can become something really cool and hopefully he'll be able to explore his ideas even further.