A bizjournals article (https://www.bizjournals.com/orlando/new ... orida.html
) from a few days ago includes an image (credited to Brightline) that includes the first concrete indication of how they will connect between MCO and WDW. It also mentions that they are interested in sharing these tracks with Sunrail and running commuter trains on them.
1. Sharing a route with Sunrail south through Meadow Woods
2. Then west along Highway 417
3. Then west along Highway 536
4. To a station on-premesis at WDW, which to my eye appears to be somewhere roughly between Epcot and Disney Springs
5. Sunrail terminates there and turns around to head back toward MCO; Brightline appears to reverse as well, but then turns south along I-4 to continue toward Tampa.