The NFL's Injured-Reserve (IR) list was created as a way for teams to make room on their roster for a healthy player while maintaining rights to an injured player under contract.
Among other things, a player placed on the IR receives the remainder of the money owed to him in that season, but is no longer eligible to play for the remainder of the year.
The NFL is currently in negotiations to tweak that rule, allowing a player to return to the roster from the IR at a point in the season.
Currently, a player on the 53 man roster stays there unless he is released or placed on the IR. This differs from Major League Baseball, for example, where a player is put on the Disabled List, thus, not counting on their 25-man roster. MLB can have a player not count on their active roster for 15 or 60 days, so they can bring in a replacement while that player recovers. The NFL's policy does not allow that, presumably, to stem the desire of a team to stash a player away, not having him count against their roster but not having to risk letting him go either.
While the details are yet to be hammered out (two of the biggest details being the length of time a player must spend on the IR before being eligible for reactivation and compensation for that player while on the IR), but this rule would help a team deal with a player's injury in a less-than-absolute fashion, and allow some time for rehabilitation and healing before making a definitive judgment on his availability the rest of the year.
The most likely injury this would create flexibility with would be concussions. Those injuries vary so greatly in terms of severity from player to player, and it's difficult to determine how long a player may struggle with that injury. This would allow a team to place a player on IR for several weeks, and have him rejoin the roster when he's functionally and safely able to play again.
The league is also in discussions with the union over moving the trade deadline back from Week 6 to Week 8. The idea is to allow a bit more time for trades to develop, and have the playoff picture a little bit more defined before disallowing teams to pursue other players.