And also:

There is no currently no firm plan to do anything in the short to mid-term with the shuttered portion of Concourse C, other than to use the gates for DCI hardstand / RON parking and GSE storage/staging area. When DL initially proposed to shutter the north-end of Concourse C a few years ago one option was to demolish the closed portion, but the WCAA's decision firmly was no. DL had to take a write-down on the shutter portion of the terminal that still wasn't depreciated. The airport did fill-in the ramp area north of Concourse C to make an area for DL to use for hardstand / RON parking, which was needed, particularly since the 4R de-ice pad has been used for that purpose, but they can't during de-icing ops.

Concourse C is still used fairly extensively, but its a function of the highly-banked nature of DTW. In particular, during the larger banks during the big morning departure bank from 8:30-9:30, and also during the big evening departure banks at 5pm and 8pm that have significant number of CRJ-200 departures. In the early-evening, not uncommon for almost every gate on C to be used. Middle of the day the departure banks are much smaller and they don't need to use much of C. Gate utilization is pretty low though, and I'd guess the numbers are somewhere around 3-4 departures a day on average.

They have reconfigured several of the gates on C to fit CR7 or CR9 sized aircraft, but respacing and removing about every 3rd or 4th gate on each side. Some of the gates, particularly the ones that are attached to the old ground-level hold room are CRJ-200 only gates.

In the most recent master plan, there are options proposed to how they could repurpose Concourse C to fit larger aircraft if the demand ever makes it necessary. Essentially, the preffered option would be to fill-in the "nodes" between the gate pods to make for expanded hold rooms and concession areas and reconfigure the parking positions to fit up to 717 sized aircraft. However, there is no plan to do and the demand in the near term doesn't justify doing so.

TL/DR - Concourse C is still needed in reduced capacity and no plans to do anything diffferent than status-quo at this time.