I think the prevailing opinion is that there is going to be some manner of 'for pay' version of Magical Express, but no one really knows the details yet. I'd give it some more time to see what develops before you make your decision
For SSR you could do a one way rental car. We have done this many times but in the opposite direction SSR to MCO. There are many car rental companies within walking distance from Disney Springs. At the Hilton across the street from DS is a Avis car rental location. The WYNDHAM RESORT across from DS has a Dollar rental car counter. And just up the road from DS is an Alamo rental location at the Holiday Inn. You can rent the car at MCO drive to the resort drop off your luggage then return the rental car to one of the locations by DS. Walk across the street back to SSR. Best thing of all, in Florida there are no one way rental fee's when picking up at one location and dropping off at another. We have used Avis and Dollar a few times never had any issues and it was easy. The rentals were around $26 for the day. This option also gives you the ability to stop at a store to pick up snacks, a case of water or whatever you might need since you get to keep the car for 24 hrs. Because weather you rent for 4 hrs or 24 hrs the price will usually be the same amount so you might as well keep it for the day and take advantage of have a car. And the next day if you happen to need anything before you turn the car in, there is a Walgreen's 5 minutes from SSR that you could stop in and get what you might need. And still have time to get the car turned in to the rental car company.