Nobody has unified field theories yet but could dark energy if considered as a field be useful in this endeavour?
Probably everyone who has ever attempted some progress in grand unified field theory has also considered the issue of dark energy and whether their work has any bearing on it. If indeed there is a non-zero cosmological-constant-like term in the Einstein field equation, as cosmological evidence suggests (but does not establish beyond all reasonable doubt), then a natural way to suggest how it comes about is by appealing to the nature of the vacuum presented by almost any quantum field theory. The problem is that if one does this in any of the most straightforward ways, then one gets either a prediction too large by many orders of magnitude, or else the prediction zero. It is hard to get anything in between.
As things stand at the moment dark energy is not yet offering any useful data to attempts at generalized field theories, as far as I know. But, as I say, it is natural for anyone working in theoretical physics to be aware of the issue and see if they can make any use of it, or offer anything towards better understanding.