I recently was at WDW and this seems to line up perfectly with what a cast member told me. This CM was working in Watto's Grotto, (a Star Wars pop-up shop on the top of SOA and near LMA) and said that the store would be closing in the middle of April. HISTK playset is also closing mid-April, and WDW would not needlessly close down one of the few places in the park for younger kids without really needing to. Add onto that the shuttering of LMA, and something is obviously going on in the top part of the park. The CM said that SWL construction was starting "in the next month" (he said this at the end of March) and would be located around LMA and SOA. He also said that the Muppets would stay put, which is yet another thing that lines up with your map ^. He also said that there would be a full size Falcon (we all knew that already) but that there would also be a full-sized X-wing and a full-sized imperial shuttle (he claimed it would be the "real kind, where the wings go all the way up and almost touch, not like Kylo Ren's" whatever that means). Also, when I was there, a construction wall was put up bordering Cypress drive around Muppets and the back of SOA. I think Phineas and Ferb meet and greets and a coffe cart used to be there. Keep in mind that this SWL info is just what I heard from a CM and I do not claim to perfectly know what is happening, just thought I'd relay what I learned.
But having SWL in the top part of the park makes sense. As someone above said, WDI can repurpose the frames of SOA for the "street market" area we've seen in the concept area. Putting this fully immersive land (with seemingly high mountains surrounding it) probably wouldn't work great around the Echo Lake/parking lot area as it would probably be pretty out in the open. Also, the fact that there are so many closures in the LMA/SOA area really leads me to believe that that's where SWL is going to be.
I don't think this spells the doom for a "phase 3" though. They could still expand out in the echo lake/wetlands/parking lot area for something, or possibly go up to the backlot tour/catastrophe canyon area. Although I really hope they fix up Future world before they do a HS phase 3.