Yes, there will be a permanent base. All we are planning at the moment is to make this the hub that you work from to launch missions. No upgrading but it will be the place you can house your characters and subs you've found.
It's very possible we could continue to add features to the base but that's not the plan for the moment. The team is too small for me to feel comfortable adding a lot of new things into the scope and trying to keep a release date in the first half of 2018.