The solution for a quick build is rather simple, leave the 528 at Monument Parkway, join the OUC RR or the right-of-way as it angles southeast to the 417, following that to CR530. The OUC line joins the SUNRAIL route just below Sand Lake Road and would make it possible for some of the future trains to enter downtown Orlando/Winter Park, as well as allow SUNRAIL to operate future commuter runs to Cocoa between AAF trains. This type of railroad operational agreement is done all of the time.
Originating and terminating at OIA might work for AAF, but entering the downtown core (which is rapidly expanding) would make it more attractive. The Sunrail to AAF transfer at the airport is going to be a unnecessary inconvenience considering the strength of rail is not the ability to 'fly non-stop' but to serve several cities in between (which could be done with 5 trains out of 20 for example. Those 5 would be the trains that carried Florida residents and businessmen. They way they have it planned now it is only going to appeal to mice in the long run.