Adding PostgreSQL is in the suggestions section of the panel. This is the link to vote for it (costs you 5 points).
I could be wrong, but I thought one of the honchos mentioned it here at one point and said it probably wouldn't happen. Not sure if that's still the case, but if it is, I don't know why they'd bother adding it to the suggestion area.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.