Honestly, I'd say this sort of tactic is definately within imagination and the spirit of the rules. Its very easy to envision a great sword wielding fighter body checking, shouldering, and throwing himself at his foes - paints an awesome picture in my mind :)
First off, the only builds this change can threaten are other fighter builds. Most other classes are untouchable when compared to our basic beatstick so I doubt the status quo is gonna be rocked by allowing your fighter to boot someone he skewered with his big sword.
In order for a 2H fighter to take advantage of this ruling he would require 15 Dex minimum. This MAD cuts into the characterss dependency on an even Strength score modifier. In 25 point buy this moderately high Dexterity is gonna eat up 8 points; coupled with 16 in Strength that only leaves the player with 7 points to distribute in Con and his mental stats. Plus, at lower levels that +2 Dex mod will probably be subsumed by platemail - further diminishing the impact of his spent points.
Furthermore, if he ever wants to increase the effectiveness of his goofy fighting style he'll have to pump up his Dex (While sacrificing his Strength) - a stat whose effectiveness is limited by the 2H Fighter's traditional reliance on heavier armors.
Now, what does this character gain?
He'll have a second attack that deals roughly 1d6 + 1 damage (Rounded down from 1.5). Recall - these armor spikes cannot be power-attacked with and do not benefit from leap attack.
So, our character (At first level) takes MAD right to the face, looses a feat (Probably Cleave - or Great Cleave if human - a feat that is at its most glorious at the lower levels) and takes a -2 penalty to attack rolls for an off-hand attack that doesn't synergize with his fighting style.
Personally, I'd say this build is far from broken.
