PS2 BC came in handy to me when I bought my PS3, as I didn't have a PS2 before and well there was a PS3 game drought at launch anyway, so I bought and played the most interesting PS2 games
I won't need PS3 BC in a PS4, as I already have a PS3
btw, a "PS3 BC add on" would have to include the Cell, probably the RSX and the XDR and GDDR3 ram .. I doubt you can manufacture something like this for only "$50-100", as production for all of those items is being phased out and hence is becoming more expensive







