PS1 boxcars tend to be tall compared to other scale boxcars like AARs. I think they will look funny with traditional cars mixed in since already they stand out with scale box cars like they should.
Theses new sound cars to me are all you really need with the min/max setting and volume control. Most of us will not be hitting the dialog buttons for loading and unloading too often like on the vision line cars. Transposing the sensors and electronics into a traditional box car would be a good option assuming the fatboy speaker will fit. We won't know much much until we see them in person but like others mentioned, go to your local hobby store and look at any recent lionel PS1 boxcar and see if for yourself.
I have a feeling these cars will be great sellers and I will order a few myself knowing that I do not to like the look of the higher PS1s (even though they are prototypical). If I surround them with lower cars like flats, gondolas, or hoppers, the extra height is less noticeable to the eye if that bothers you.
If my predictions are correct, and these are good sellers, Lionel will make more of them perhaps in other boxcar types which are lower and may be even into hoppers or tankers, and hopefully into traditional sized boxcars too.
This is a no brainer for our trains and hopefully Lionel will crank out more types of cars with freight sounds both scale and traditional sized.