It's open to everyone, I saw numerous guest walking right up.
It's honestly a lot of fun. Significantly better than it's original incarnation. If you love Tron, you'll absolutely love it. The ride portion is obviously almost identical but with a new overlay on it. There are definitely some improvements though. There are a lot of large plasma screens and projectors that really add to the overall experience. The whole process is really fun, from start to finish but I honestly had the most fun with my personal design after the ride and it looks like they have more plans that what is currently working and could easily do more with the concept. The post design scenes, i.e. making your own Chevy car commercial with your car is hilarious. There are numerous narrators, locations, music, and messages (power, eco-friendly, cost, etc.) for the commercials and it's a lot of fun to play around in.
So here is what everyone wants to know, if you are a guest how do you enter? Swing to the far left and head towards Mission Space. You'll see Test Track and there will be Cast Members with the gate open. If they are not checking for I.D.'s than anyone can ride. I maybe waited 20 minutes. Not sure what other wait times looked like throughout the day or if they were originally only having it open to CM's but it was too dead. Point being, if you are in Epcot, it is worth a try. I imagine that it was open to guest all day but they were keeping it hush hush enough where they had guest on it, but not bombarding them. Until the front is actually open, it will probably stay rather low-key sans communities like us.