Before you get overly connected to that $10,000, consider how much of a loss that builder has already suffered on that unit between the time it was previously in escrow and now. At the retail price of the upgrades their loss is a lot more than the $10,000. Now project that rate of loss over the next 12 months.
Taking a $10,000 hit right now is definitely the better choice compared to what’s going to happen to your financial position if you buy that house now. At some point it is not unreasonable to think that house could lose $10,000 in value every couple of months. An annual loss of $60k is not at all beyond the realm of reason.
Stick around for a while I’m sure you’ll save a ton of money on that house.