Until this officially starts up, we're just speculating, so I'll add my speculation to the mix.
1. There are numerous legitimate reasons why someone might not catch the first bus out on arrival at MCO, such as waiting for others to arrive on another flight, need to hit the john, grab a bite, recover from air-sickness, etc., etc.
2. Disney wants to make sure guests and their luggage are both at MCO at the same time, not separated due to lost baggage, passenger getting bumped to a later flight, flying early on stand-by etc.
3. Disney will hold luggage until one or more party members 'checks in', and here's the crux of the matter. Will the check in be at a central station remote from the busses? I think so, and if so, one only needs to leave the plane, go to this location, check in then do what they will, be it getting on the bus or giong to WDW in another fashion. I don't see Disney waiting until everyone who checked in gets on a given bus as there will be many instances when someone does the check in and then wants to take a later bus for the reasons cited in #1. I see Disney's interest in making sure you and your luggage are there at the same time, I don't see them spending time and effort beyond that.
4. If Disney wants to actually see you on the bus before releasing your luggage, I see only one efficient means of doing it. They could have hand-held barcode readers to swipe your portion of any ticket you received with your luggage tags. These would likely be WiFi devices that instantly send the info that you arrived to a central computer that then releases your luggage. The glitch here is, what happens when, not if, someone looses their tag? They'd need a kiosk or desk to handle these exceptions. This technology is not cheap. I'm a programmer and I've worked on such things in the past. I just don't see Disney spending the extra bucks to track us right on to the bus.
All our questions will be answered in a few short weeks. Our next trip is next March so I'll have plenty of time to see if this works for me. We will arrive just before 9 am and my goal is to capture the first day. If I can skip the baggage carousel, hop a TownCar to our resort and check in quickly, we can be in Epcot before WS opens.
Bill From PA