I know many are passionate about the real estate practice, I acknowledge that and am knocking it! 

Plus, it appeals to both investors and homeowners because of its practicality and aesthetic appeal.

In practicality, your lease is saying that you have the legal right to charge the rent up until you find a new tenant because you have a legal obligation to mitigate your losses.

Are there any practical methods for implementing usage-based billing without submetering?

I don't doubt the practicality and workmanship, however the design doesn't do it for me.

As standard practice I offer my best pricing the first time to not have to go back and fourth like a car salesman to win business.

It's just that those other agents didn't like their business practices.

I know for most this isn't practical, but for the one's that can do it-- do it.

The drawback I have is that it is difficult to pounce on properties that are still selling relatively quickly with the commitments I have  to my patients in my dental practice.  

Yes, market is volatile, interest rates are fluctuating, but the fact that we can't neglect is that banks are more regulated, lending practices are stricter, and the housing market is not based on a pile of risky mortgages.