The heated seat hardware isn't expensive, the blocks can be bought for about $15/chair second hand on their e90 range. I highly doubt it costs BMW any more than a couple of months of the rental cost and I strongly suspect over the life of a car they will get at least a couple of months rent and justify the cost.

I, for one, welcome this change. BMW makes retrofit kits for everything because they know people want features that aren't in their spec and they're very expensive. I buy old, second hand cars and I'm at the mercy of the original buyer when it comes to features included. This way, not only do I get the option of a feature that was never bought, but I can enable it only for the couple of months I'd actually need it. Or better yet, I'll do what I do with everything I own and hack it, unlocking everything I can.