"Will I need a Gizmoplex Pass to use the Gizmoplex?"

No! Members will get access to extra content and all live events, but many Gizmoplex features will be available for everyone to use!

Taken from Backer Update #15:
https://www.kickstarter.com/projects/mst3k/makemoremst3k/posts/3178709

No! Just like your local cineplex, the Gizmoplex will be open to everyone... but there will be a lot of membership benefits that come with an active Gizmoplex Pass.

As of now, the Gizmoplex will give all visitors access to...

• A PERSONAL VIDEO LIBRARY of episodes you rent or own.
• A PRIVATE THEATER to watch your episodes + host watch parties.
• The VIDEO COUNTER, to rent or purchase more episodes.
• The LOBBY, where you'll be able to view the "wall of backers."
• The TICKET BOOTH, where you can buy tickets for live events.

All of those features will be available to everyone... so if you don't want to pay for an ongoing membership, you don't have to. You're free to buy and rent only what you want to watch!