I spoke with MDB about this. She is in a particularly good position to get the dirt on the topic, being that where she works, she is in constant contact with the parks and rec guys.
First of all, one of the conditions of the grant, was that there would never be a fee for entry, so don't worry about that.
Second of all, the no diving signs are temporary. Obviously they intend to allow diving, they put in a lot of features that are scuba specific.
As an employee at a park that's undergoing construction, I can say this... Any part of the park that is under the care of the construction company, is off limits to the general public. It's not the matter of the bathrooms not working, it's an insurance thing. If a diver goes down there, and gets hurt while a contractor is "responsible" for the area, they can be sued. So, until construction is finished, they don't want ANYONE down there, including divers.
That being said, you will never keep everyone out. They signs go up, the cops and guards can be posted, but people will sneak in. They have to show a reasonable attempt to protect the public from themselves, in case of legal actions.
All that will happen, by having divers sneak in there before the operations are finished, is divers getting a bad name. The law makers will paint us with a broad brush, unlawful trespassers, unable to abide by the rules.