That looks like a Softride suspension stem. It's a great design, but it was never a big seller, despite the fact that racers using that stem won the mountain bike world championships and mountain bike world cup in the same year. I guess people just liked the he-man look of a suspension fork better.

I agree with those who were recommending adding a clip-on aero bar. I've been using that setup with my mountain bike since the early 1990s, and it's terrific. Nothing changes except that you can ride comfortably in a drop-bar-like position whenever you like.