Kate Beckinsale's real-life hubby Lin Wiseman who is also the producer/director for Underworld talked to IGN at Comic-Con and told them this;
It's all being written and talked about and hopefully all comes together. So we're weeing how things happen. But we're all keeping our fingers crossed."
He says this about Beckinsale's return;
"Yes. That's the plan. we're both waiting to see what kind od story comes together. It's just getting the script to a certain place we're both happy with.
I'm excited about Underworld 4 aka Underworld 3D, let's see where this goes!