I don't know who's interested in preserving this equipment; your guess is as good as mine. Perhaps a preservation group from here in NY may save a few, being that they also have cars stored on the NYCT property at Coney Island Yard. It is also inevitable that the Transit Museum may hold some of it's own. I talked to the former curator about this some years ago, who said the Museum was going to pick out Redbirds for preservation. Times have changed since then. I'm uncertain if this is still the case.
So far, there's a pair of R-26s slated to go west to Illinois. A Branford acquisition is not out of the question, but uncertain. I have little fantasies, but that's all they are, merely fantasies. What you want, and what can actually happen are two different things.
In regards to Railway Museums, Danbury is a Conventional Railroad Museum, interested in preserving the larger railroad equipment with a New Haven Theme. NYC Subway Cars wouldn't fit in that picture. The Illiniois Rwy Museum is an exception. They preserve streetcars, rapid transit cars, and the heavier railroad stuff. Not every Museum will do things the same way. The theme of preserving equipment varies.
With the exception of the Danbury Rwy Museum, the MTA Trackage does not connect to any other Museum in the NY Area. Even if a NYCT subway car was transferred to New Haven by Metro North for Branford, the car would still have to be trucked a short distance, and this would cost money. Nothing's for free my friend. The acquisition of a rail vehicle is the sole responsibility of the Museum in question. I don't think that the MTA is into gift giving. For them to do this, they must benefit.
One can't help but wonder what the MTA has donated to Danbury. FL9 #2013, formerly of Metro North, was acquired by them recently. Did Danbury pay for the rights to the unit or was it a simple write off?
-Stef