I'm joining this discussion a bit late, but here's my prediction for a layout of the future:
The layout itself won't be designed primarily to be viewed by the naked eye (although that could remain an option) but rather by TV and/or virtual reality. A typical layout would be a trough, perhaps 1'-2' wide (depending on they layout's scale) encircling the layout room. It could be built at floor level, or near the ceiling. The track essentially runs down the middle of the trough, with backdrops and scenery on both sides.
Running the train will be by using controls mimicking a real engine, only with a TV monitor replacing the view ahead. Small micro-TV's will be in the model engines, with the signal perhaps mixed with a Simulator program to make it look like the view is from the interior of a real cab, with the TV signal showing the layout visible only thru the windows. (You could substitute the view from a caboose with a similar micro-TV so you could look out over the train from the cupola, or from the interior or observation platform of a passenger car.)
You operate the train like a real one, and what you see on the monitor is pretty much what you'd see from a real engine. Blue- or Green-screen technology would allow your sky backdrops to be animated, so clouds actually move, rain clouds appear, and you can connect that up with your lighting to simulate the progress of the sun in the sky.
Another viewing option would be micro-cameras mounted at prime viewing spots beside the track or in a signal tower. The view would be shown to the viewer via a TV monitor, but you could also have a helmet that allows for "surround" virtual reality viewing - and is also tied into a servo that moves the TV camera around as you move your head around. (This could be used for the cab and other viewers / operators too.)
There would be much more animation than today...scale people wave as the train goes by, automobiles roll along roads, etc. along with sounds coming from small speakers under the layout, or just piped into headphones as part of the virtual reality system. The train goes by a farm, the sounds of cows mooing becomes louder, then softer after you pass.