Great idea, and this has been added to the roadmap.
In the meantime you can implement a simple version of this by making these two substitutions in qa-db-points.php:
COUNT(*) AS qvotes
... to ...
SUM(vote) AS qvotes
... and ...
COUNT(*) AS avotes
... to ...
SUM(vote) AS avotes
This will modify things so that users gain points (as per the setting in the admin panel) for up voting, and lose that same number of points for down voting.
To make a down vote lose twice as many points as an up vote gains, you could use something like this:
1.5*SUM(vote)-0.5*COUNT(vote) AS qvotes
... and ...
1.5*SUM(vote)-0.5*COUNT(vote) AS avotes
Or for a down vote to lose half as many points as an up vote gains:
0.75*SUM(vote)+0.25*COUNT(vote) AS qvotes
... and ...
0.75*SUM(vote)+0.25*COUNT(vote) AS avotes