First off, I don't regard this as 'my' project. It would need funding, which I'm unlikely to be able to get. It might need someone looking for a research project, and with access to an academic grant, or a media company. So if you know anyone who dances tango and happens to be looking for a research project, or who has access to funding... Just so long as the resulting footage can be available on DVD, with some of it posted on YouTube for everyone to watch.
The project is to set up a series of small, informal milongas in Buenos Aires where the very best social dancers of the older-generation tango dancers can be filmed dancing in a setting that is familiar to them. Something like this was done for tango music with Cafe de los Maestros, and I think it should also be an urgent priority with dance.
Almost everything danced by the generation that learned social tango in the late 1940s and 1950s has been watched and copied, and is currently taught. What cannot be preserved, except by video, is the way that generation dances, with its roots 50 years ago, before the tango hiatus, and with a lifetime of experience. That's an inspiration, a source that can be preserved for the future with video, and which will, very sadly, soon vanish. It's not what they do so much as the way that they do it, that tenuous link with the past that needs to be preserved.
The only way I can think of filming this clearly would be by setting up a short series of small-scale milongas in Buenos Aires, perhaps late afternoon or early evening when a familiar venue might be available. Of course, the venue would need to be reasonably well-lit. The participants should be paid to attend, on the agreement that they will be filmed. Filming should be discrete and shouldn't intrude on the social dance: no one wants camera operators waving cameras around the dance floor. The set and setting need to be conducive both to filming and to normal social dancing.
It's wonderful that videos of social dance are now being made, but in a social milonga it's not always possible to give a clear idea of what is happening. Of course the cameras are never going to capture everything but they can show a lot. Moreover, as David Bailey commented recently, it would do a lot to raise the profile of social dancing outside Buenos Aires, where few people have had much chance to see what the best social tango looks like. It's never intended as a show, but it can still look marvelous, and continue to be an inspiration.