let the film days, F90x and below = amateur, no mirror lock up.
F100,F4, F5, F6= professional, have mirror lock up.
DX becomes amatuer range and FX for pros.( or the rich amatuers)
nikon will keep DX, provided that all other camera companies continue to keep their crop sensor cameras.
this way, FX cameras will have a better price point for them to get a better profit. If DX is gone, there will be a big hole and FX price will have to come down quite alot to fill the hole.
but if just 1 company decided to go all full frame and shift the FF price down 1 scale, competition kicks in and DX will soon follow the exit.
seriously doubt anyone would do that since there is alot of research money that the companys need to earn back.