The more I think about this, it kinda makes sense. The current pay grades for leadership (at least in my neck of the woods) starts around 14/hour. IF the goal is to get the base rate to 15 by 2020... then technically -in Target's eyes- new hires and TMs will be getting leadership level pay... so, by this thought process, wouldn't it make sense that they'd also get leadership level responsibility?
15 at base TM would be required to do a lot more than current TM at current base. So, shuffle duties around that normally would be held by smaller group of TM. Expect Global cross-training at $15/hour. Thin out current employees that don't meet those expectations and hire higher quality employees going forward (considering that Target will be paying more than current minimum, more applicants will likely be applying).
This is a hypothesis, and I'm certainly no business degree holder (ART BABY!), but it makes logical sense to me that Target will be separating the wheat from the shaft going forward. So, TMs that don't meet the grade will be termed, regardless of current role.