This is something Setherick shared with me a few weeks ago and I'm pretty excited about it. In the next game version slow DB's/WR's won't be so useless. I'm not in a Beta league and I haven't looked through the forums in a while, so I haven't seen it in action but it sounds good.
In 0.4.3, DBs will roll their M2M against a WR's Route running. If the DB wins the roll, then the WR won't be able to reach top speed until they break free of the coverage. In practice, this looks like the DB is slowing down the WR, but the roll takes the place of all the things NFL DBs do to throw off a WR - punch, slide, mirror, ride the hip, etc. This makes slower DBs with high enough M2M play up to their cover ability, but fast WRs will still run away from them when they break free. It looks a lot cleaner too in the game window.