Everybody saw this coming:
I still don't understand why catchers are ever allowed to block the plate, even while in possession of the ball. What's wrong with simply having a uniform rule in which the fielder may not position his body to block the runner's access the bag? If you want to avoid collisions, that's the rule. It isn't complicated. If the only way you can field the ball is by obstructing, tough luck. There's no such thing as a throw that can only be fielded by blocking the back. You can always take a step in or a step back. It might not be ideal, but you don't HAVE to interfere.
Nobody who learned the game of baseball with the rule above would ever think the game would be improved by allowing fielders to interfere. The runner has right of way to the bag. To get him out, you tag him with the ball. If you obstruct his path to the bag with your body, he's safe. It's simple. It's elegant. It encourages skill and precision. The only downside is for people who would rather watch football and for people in the game who feel like "their" game is being taken away and/or their toughness is being devalued.