Oh absolutely. You can turn around a small plane in under an hour, a feat you'd be really pushing to do with a 380. Even refuelling for a long haul can take longer than that.
And different constraints apply to different airports. If you have plenty of gates but no landing slots, like Heathrow, you don't mind if the planes hang around a little longer. Atlanta would have the opposite issue with their 5 runways, which could theoretically fill all their gates in just over an hour.
I was always wondering why no one has started using 6/7 doors for loading/unloading. You could get all passengers on/off in less than 10 minutes each, the doors are there.
Cleaning is just a question of how many people work on it and refuelling could be done by 2 trucks I guess? At the moment they just don't need it because the plane won't be turned around faster anyway (boarding with 3 doors takes 20+ min alreay).
I think it's just not worth it. Gates would have to be redone at huge expense with aerobridges on either side, and the technical challenge of putting the bridge over or around the wing somehow would be formidable and expensive. Airports would be loathe to eat the cost. And unless you very tightly controlled the passenger load order and which side they were on etc, there'd just be chaos on board anyway with people colliding after loading from the wrong door.
I think the fact is that even though it annoys us as passengers if it takes 10 minutes to get off the plane, it doesn't make all that much difference to the turnaround time. There's still fuel onload, baggage and cargo off/onload, catering (which uses the back doors currently), waste materials offload, technical checks.. there's a certain irreducible amount of time it will always take, which increases with the plane size.
The fastest I've ever seen a flight turned around was about ~15 minutes (a late 737 trying to get away before a storm hit in Sydney), skipping catering, cleaning and my bag. I've heard SouthWest aims for about 25 minutes, but they had to get rid of assigned seating and be pretty strict with carry-on luggage to achieve that. That seems like the most optimised anyone's going to be able to do, and that's exclusively 737s.
I've heard of refuelling being done with 2 trucks though. It can take 2 hours to fuel a 380 going its maximum range. If a plane was an hour late and they needed to turn it around fast to meet a curfew, that's something they can do. Wouldn't be worth it with narrowbodies which can be done in 15 minutes.
Why not use stairs? Many low cost carriers do that for smaller planes. People who don't want to walk stairs can still wait and exit via the front but others will appreciate getting out quicker. Many business travellers only use carry-on so that it doesn't matter to them when luggage comes out. And even a business class in a A380 can currently take long to deboard.
Using stairs is usually safe enough, the left side of the plane tends to be clear and having one person monitoring that no one leaves the area is sufficient.
And different constraints apply to different airports. If you have plenty of gates but no landing slots, like Heathrow, you don't mind if the planes hang around a little longer. Atlanta would have the opposite issue with their 5 runways, which could theoretically fill all their gates in just over an hour.
It's a fairly interesting optimisation problem.