Any new E-ticket would help but I really do not think any attraction using a simulator/motion base (even if a vehicle moving through a show building like a Scoop or Indy) will be distinctive enough from RotR and SR or achieve the visceral thrill of a coaster. I think it would be a mistake to spend hundreds of millions on anything other than a coaster to "save" SWGE. And if they can't do a Cosmic Rewind scale coaster, I'd still take a Seven Dwafs-scale, particularly with a Jawa Droid Factory theme which does two things: highlights a key merchandise category (droids) and brings a fan-favorite Original Trilogy element (Jawas) into SWGE. (It's easily explained they live on Batuu too.)
I know this is a SWGE discussion specifically at DHS but I did an exercise below with Disneyland's SWGE as a "worst-case" assuming they need to treat both parks equally, so if it can be made to work there and all the impacts mitigated, it allows for this to happen at DHS. My assumption being if they can't do it at space-constrained Disneyland, it's a no-go at both parks.
It is possible to squeeze the Cosmic Rewind gravity building can be fit in without taking any more backstage, as seen in these images and a review of scale using Google Earth. From what I can find, the CR gravity building is about 140 feet tall and the Cars Land rock work is about 125 feet tall, so it's possible to have a sheer cliff of rock work (also similar to what hides the Frozen show building in Fantasy Springs) to hide the structure.
It's also possible this new mountainous structure is blended out with foreground/foothills where the Fantasyland Theater is to mitigate its visual impact. I have ideas on how to handle impacts to Toontown with a new city skyline but that's getting too far afield from DHS SWGE to describe here, I'm sure this has pushed the topical boundary enough.
Overall, my point is I think a great coaster -- something akin to Cosmic Rewind -- could be an addition to both SWGE.