Split boarding or two-door boarding sounds at least to me like a no-brainer. Basically you open both the front and back doors and let passengers board from ends of the airplane. Seems at least to me it's a lot more common with the terminals that use air stairs that you need to walk across the apron to get to rather than jet-bridges, as it's pretty easy to just roll two air stairs up to the aircraft.
Why isn't this more common? Boarding and deboarding a plane is slow and very prone to a single person holding up the entire process as there is no room to go past them in the aisle. Allowing boarding from both the front and back doors will at least half the time it takes, and especially with deboarding, gives passengers two options for exits which means a single person can't hold up the entire plane. If the people in front are being slow, just leave from the back.
I know that designing a jet-bridge that can line up with the back door is pretty difficult especially since you have to fit it alongside the jetbridge for the front door, but why not just use the jetbridge for the front door and roll air stairs up to the back door and have half the passengers go down to the ground and walk across the apron? I'll gladly spend a few minutes walking through the heat or rain if it means we can board and deboard in half the time, especially if it means we don't lose our takeoff slot from a slow boarding process and have to wait on the tarmac for even longer.
What do you think? Are there practical issues that this is not done more often? Or is it simply because the airlines don't really want to pay for more gate services?
Here are my thoughts.
One part certainly is that you need to pay for more infrastructure, without a real benefit for the airline. Passenger boarding/deplaning is not the bottleneck for turnaround. Evidence: after boarding, you normally sit around for quite some time before the plane starts moving. You also need a flight attendant at each door, who is then bound up and cannot perform other duties.
With airstairs, it's different, because you often need buses, and you always need security personnel, and the faster you get all people off the apron, the better for everyone, so in that case, time is a factor.
Using airstairs in combination with the jetbridge introduces the security angle again, so you basically have the worst of both worlds, and have to pay for the jetbridge privilege and for security personnel. And if you don't separate the passengers by row properly, you won't even gain a lot, because more people have to pass each other in the aisles. As you have found out, passing through the door isn't actually the bottleneck, but stowing carry-on luggage and finding the right seat, and waiting for the aisle passenger to get up and let you get into your window seat.
P.S. I don't think it's a good idea to post this to two different communities. If you want to reach both, just post a short link to the discussion on the other community.