A few points on the security bubble. The security bubble does not/and did not intend include the hotels. Paradise Pier, Disneyland Hotel, and the Grand Californian are all technically outside of the security bubble. I never saw a proposal to move security to the lobby areas of those hotels. The Grand Californian has a security checkpoint located within the hotel adjacent to the special entrance to Disney California Adventure. But families only need to go through that when they are actually entering the park. All individuals entering Downtown Disney, Disney California Adventure, and the Esplanade are required to go through security. But you only go through it when you're attempting to enter the park.
Around the time that the Eastern Gateway was proposed, Disney pushed the security bubble westward to encompass all of Downtown Disney. Disney had a similar aim on the east side of the resort. The following picture illustrates the proposed locations of the 6 security checkpoints.
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The red lines represent the locations of the proposed checkpoints. The blue line represents the bridge. You can see that the four security checkpoints on the west side of the resort all came to fruition. To enter Downtown Disney from the hotels, you need to enter either security checkpoints 1 or 2. To enter California Adventure from the Grand Californian, you need to use security checkpoint 3. After parking at Mickey and Friends (and now Pixar Pals) you go through security over at checkpoint 4.
The two checkpoints I've numbered 5 and 6 are the ones that were torpedoed by the demise of the Eastern Gateway project. Checkpoint 5 would have been a small checkpoint exclusively for use by individuals parking at the Toy Story Lot. The location is a little rough, but it's the general idea. Checkpoint 6 was the real controversial one. That checkpoint was the one where all the people using the east garage would have entered.
If Disney actually wanted to integrate Garden Walk into their plans (I'm dubious but anything is possible), they'd have to have two security bubbles that were disconnected. I don't think there's a way to have an uninterrupted walkway from one to the other without use of sky bridges. A monorail, bus, or gondola system could link the two parts without leaving the bubble though.