It's no secret that I am also quite concerned about temperatures inside the Skyliners, especially in the summertime; if you were to be stopped for more than 10 minutes or so out there in the direct sunlight, I fear it might become very uncomfortable.
But... maybe not. I'm not a good judge of temperature, given my personal sensitivity issues, as well as my PMLE. So, what is horrifying for me might be only mildly bothersome to others. I always presume (until I can judge otherwise) that I am going to be "that person" who is always too cold, or too hot.
In the video that was posted above, we see the Skyliner stop for ?maybe? 3 to 5 minutes? and they all seemed fine, and we *know* how hot it is down there this time of year.
As far as trash/food/spills, etc. goes, I feel like
@gap2368 is correct - it will be no different than the monorail or the buses. (or the boats, for that matter) There may be some accidents where someone spills, or some trash gets left behind in the rush out the door at the station, but I have a feeling that overall it's not going to be a big problem. If a particular unit got to be too messy (say from someone being nauseated) I imagine that they could loop it as "out of service" where the doors don't open around to a barn/storage location where it could be taken off the line and cleaned. And they may even just do that in the HA loops between Guests. Who knows?
The screens will prevent people from dropping things out the windows, so no worries there. I was glad to see them just so that Guests who ride don't have to worry about hitting a cloud of Love Bugs this time of year!
In time, I have a feeling we will see some landscape remediation occur along the path that will help hide the trails of gravel beneath.... but frankly, I think most Guests won't be looking down unless they are out over the water, and maybe not even then. And as far as the poles go, I remember a lot of adults who thought the Monorail was ugly as sin when WDW opened all those years ago. I rode it for the first time in 1972, and as a kid, I thought it was the most wonderful, glamorous way to travel around Disney World, ever. Now a whole new group of travelers get to have that same awestruck feeling as they go soaring off over the landscape on the Skyliner.
I may ride it from time to time in the future - I probably won't ever be one of those Guests who plans their transportation largely around the Skyliner, but that's OK. For the people who are excited about it, however, I am happy. I hope they get that same happy heart that I have when I ride the Monorail to this day.