So a thought just occurred to me that SSE is closing right after Memorial day weekend. Disney typically considers that weekend to be their official "Start of Summer" and have opened a few attractions over the holiday in recent memory (SDMT, Pandora, SWGE - DL). The courtyard is looking great right now and testing is underway.
I'm not saying that we should expect this ride to open over Memorial Day weekend, but with SSE closing, the park is going to need the ride and if it's ready i'm assuming they'll want to open it ASAP. I'm just saying it wouldn't surprise me in the slightest if shortly after SSE closed, Rat opens.