This is the next level of skin design. Just wait for Eric to start designing the engine and inner parts of the car. It will be the SICKKEST SICKNNESS of the Sicking SICK. Just sick.
If they have the same SkinNameALPHA.dds file in their skins_dds folder they WILL see the same effect. Other players without the file will see the default (skin not found skin) or whatever JPG was uploaded to LFSworld.
To see them the other players have to download the SkinNameALPHA.dds file manually. They are a skin so all their other skins/cars will not be effected.
However there is a side effect. You know that period of time when you are driving and your LFS hasn't loaded another car's skin into memory and all you see is a blank skin? Well unfortnuately if your using an XXX___ALPHA.dds skin your car is invisible in this moment until the other player's LFS loads the default skin or what-ever was uploaded into memory. They will see this side-effect for a brief moment until they pit/spec or stop their car for a few seconds.
Totally sucks because this means the devs will probably disallow XXX___ALPHA skins to be used to remove the glitch.