I'm all for house rules, but are you concerned with bending the success rate up and any impact on challenge level?
The dice are set up the way they are for a wash to be a failure. Given the dice are weighted to success if you move the border, as it were, for what equals failure and have a re-roll, you've bent that curve more towards success on a given check.
As I've stated several times, this is not a re-roll on the same action. It is the opportunity to make a second attempt on a later action. This house rule provides no benefit to combat checks because you can attack every round already.
