I've thought they should add this from the beginning. That being said, if they wanted to keep it really simple, they could just adjust the threshold for delaying arbitration to a number of days/games that would make it more of a decision to be weighed on whether you bring a guy up. 20 games is basically a no brainer (especially if it's a guy who won't be able to play 162 games anyhow), if it was more like half a season, you'd have to put some more thought into it.
Not a big deal one way or the other at this point, however.