I think Brightline would want to market a single-seat trip between So. FL & WDW. They're in the business of intercity transportation, not shuttling between WDW & OIA.Sooooo, for whatever reason, the current plans envisage a stub-end station at Disney.
I wouldn't be surprised if Brightline ends up running Orlando Airport - Disney shuttles and a smaller number of Tampa-Disney shuttles, with the regular all-stops trains from Orlando to Tampa skipping Disney.
I know it sounds odd, but... operationally it's going to make sense, and with Disney's "We don't want you to visit anyone else" attitude, forcing customers to backtrack to the airport in order to connect from Disney to I-Drive sounds exactly like what Disney would want.
The stub-end station shouldn't be a problem, since there are locomotives at both ends. It might just require a longer stop to reverse control direction and PTC. I believe that's fairly common in Europe.