Abdul-Rahman Sibahi, Thank you for commenting.  Your idea would certainly work and I did think about it back when the game first appeared.  The way I imagined it was simple, accomplished by linking pawns: K and Q pawns, both B Pawns, both Knight Pawns, both Rook Pawns... each a Doppelganger to their 'linked' associate. Since Pawns change files from time to time, they would need an identifier to show Doppelganger relations. 

I prefer the idea of more player control which exists in the current version.  Note - the Doppelganger Pawns are 'not random' ... the rules state:

'If a pawn is captured, the player making the capture removes it plus any one other enemy pawn (capturer’s choice). If the removal of the second piece (or pawn) causes check to your opponent, that is fine. But you cannot capture a piece (or pawn) if removal of its counter part would put your King in check.'

As to which is the better concept (pre-determined Pawn-doppelganger or Player-selected Pawn Doppelganger), that probably is a matter of opinion, like comparing Chinese Chess and Korean Chess.  On that call, I am in the minority.

Your idea is certainly logical, has merit, and would prove easier for programmers.  I sort of like coming across games that computers do not yet play... but usually it is only a matter of time before they do.  

I seem to recall seeing a set of pieces with different colors at the bases.  Pawns of that design would work with your suggestion.

If you want-I will add the variant to Doppelganger and call it something like 'the Abdul-Rahman Sibahi Doppelganger Variant' and give you credit. You could modify the pawn Doppelganger aspect if desired, based on proximity.  There are several different pawn-link possibilities. Just let me know.  Or, if you'd like to create a separate page with your rules - as your variant of Doppelganger - I have no problem with that.  It would need its own pre-set to keep the ratings aspect fair. 

Thanks again, very much, for the comment.  Best regards, Gary