I'm not sure what state the 2700s are in, but trying to get them into service until new coaches arrive would seem to make a certain amount of sense.
However, they are only 12 coaches, and as far as I'm aware, they've all had the end gangways removed, which would make them sub-optimal for running as multiple units.
A concern would be reliability. Frankly, if they were breaking down all the time, they would be worse than no trains at all.
My second concern would be driver training. The 2600/2800 units are small fleets, but at least they have common certification, so drivers certified for one can drive both. Drivers would need separate certification for 2700s.
As far as I know there are a number of 2600/2800 sets not currently in service. I'm not sure if they could be brought back into use, but that would strike me as a more attractive short term option, given the better reliability of these units, and pool of certified drivers.
However, if it was viable to bring all of the unused 26/27/2800s back into service, that would probably be around 20 coaches, which might take some pressure off the most overcrowded routes.