Awesome. This will definately switch me to premium 
I personally always try and trade foils away. But maybe have have the rules per 'category' so for example mine would be:
Mark cards tradable if more than 4
Mark all foils as tradable if more than 0
Mark all Promo's tradable if more than 1
and so forth for all the card 'categories'.
In my collection if I had 8 shocks but 1 was from 9th and 1 was from 8th and 6 then only the two from 8th would be tradable. So its not an aggregate. I am willing to collect playsets for each edition.... If this makes sense. But, other people might only be interested in playsets and not worry about from which sets they are.
Anyways. Keep up the awesome work.
Regards
Johan