There is clearly a deficit of good defensemen in the league right now. Almost every other team is looking for "A solid top 4 D-man". The salary cap also makes it incredibly difficult to add quality defensemen. So, rather than simply wait until there is some sort of defensive renaissance, how about allowing teams to ice 7 dmen a game instead of 6.
Benefits of this:
1. You can spread out minutes more, thus allowing you, top to bottom, to get more quality minutes from every dman.
2. The emergence of specialty dmen. Far too often, specialty D, such as pp specialists or defensive minded dmen, are overlooked for "not being well rounded enough". Because of out limited D icing, every D man has to be "A solid, two way, puck moving" Dman. If we allow teams to ice more Dman, you can play niche Dman that otherwise wouldn't have a job.
3. Having spots for rookies to develop: It's hard to develop rookie d men, because no matter what minutes you have them play, you're still throwing them to the fire. With an extra spot, you can chose to throw in a rookie for limited minutes, thus allowing him to slowly get adjusted to the game.
4. Every team has a better opportunity to ice a decent D-squad, thus increasing parity and competitiveness within the league.