That may be what ends up happening now with the film delayed.I also don't know why Disney is apparently so wedded to the notion that filming for the ride MUST take place during the shooting of VOL. 3. Chris Pratt's a guy who will play ball if you ask him; have him show up in a green/blue-screen soundstage in costume for an afternoon, and that's really all you need. Rocket and Groot can be achieved via sound-alikes if need be, too.
It was only going to be filmed alongside GOTG3 bc it was convenient for Disney.