Actually, it could be another layer to do smart zoning (using zoning tools to keep away AND to bait opponents into unsafe moves), and make mindless zoning/spamming less annoying.
For instance, if the roll really dodge projectiles, you could have a characters like Deathstroke in Injustice 1 keeping his original recovery frames on his guns, but still giving the noobs a tool to get in. For casuals that don't now how to dash/walk block agains spammers, it would be a useful tool, and they can spend the bar anyways (casuals tend to use the bar only for super and clash). For smart zoners, it is just another layer of strategy, a move to be target of spacing and bait. Since it costs a bar, it has limitations, a good zoner will be able to deal with it.