Realistic structures with moving figures, etc.

Don't forget about K-line! They made some cool items, a few using magnets for animation. Many of these were reissued by Lionel.

Here are a few of the original MDK versions with moving figures:

• K-42410 Operating Watchman's Shanty
• K-42407 Milk Loading Platform (and matching cars)
• K-42405 Operating Colonial House on Base
• A few variations of operating billboards

They also offered a boy flying a plan (maybe kite too?) and a moving construction worker. I'm sure I'm missing a few others.

Lionel has made station platforms with disappearing freight and people in several variations over the years.

I pull a passenger train in front of the station, blocking the little passengers from sight, then play an "All Aboard" message and press a button on the side to make the passengers disappear and when the train pulls out, there's no more people. The little kids (and some adults) love it and believe the passengers on the platform all boarded the train.

Great fun.

Some of you may recall Kramer animated O-gauge figures and scenes; I never owned any though I saw them in action at the Choo-Choo Barn.

The thing I find odd is how Lionel's scale trains have evolved to stupendously detailed models, yet their line of structures, accessories, and figures hasn't kept pace, and is kind of is, well, mediocre. There have been exceptions - the PRR's MG Switch Tower, Aluminum Rico Station, and Vision Line GCT come to mind. Fortunately, we have Woodland Scenic buildings.

I enjoy craftsman kits for my structures.  Not interested in the Lionel out of scale buildings.

Patrick, I'd venture a guess that you're not alone. Lionel has acquired some of MTH's Railking line of buildings, the brewery for example, which is a nice O-scale model. I have 3 of the Railking breweries on my layout, all of which I've mortared the bricks on.

There are a few companies, like Willard Animations, that make drop in animations.  There are also a few (though outdated) model RR books on animations.  I hope to detail some of my structures with animations and was always inspired by the work at the Choo Choo barn which was arguably some of the best animations in O scale.
I was also fortunate to purchase an animated construction section of a previous display layout (cannot remember the history now) that I have to clean up and revamp - again, a retirement project or someday project.

Perhaps the greatest concept of an operating accessory was the Lionel Backshop. I had been one of the early buyers of this accessory ~ 1999 or so, and never could get it operate correctly. A subsequent release of a new board facilitated operations. While it was lithographed tinplate, very attractive at that, the operating features were the neat aspects - opening bay doors, moving machinery and figures, and lights and sounds. Since much of it was metal, it was fairly heavy.

I can kind of see Lionel making something like this, although they would likely make it in the mega bucks Vision Line, though I think an operating coal tipple would have broader appeal.