I just think if the move is blocked, it would defeat the purpose.
I mean if I rool a 3 & 4, then I could (BEFORE SUBMITING) test many different moves / multiply moves with all my pieces to basicly determin where 2 or more of your pices are located - and in my opinion kind of defeat the purpose of the dark part of the game.
Where as if it allows you to move there, THEN if there is 2 more more pieces YOUR piece ends up in the bar - you will then only know of 1 place (insteald of multiply) where 2 or more of your pieces are located... and come with a "cost" since my piece would be put back to the bar.
Without that - I don't think it would be very "dark" nor very different then normal backgammon.