There's a theorem about a unique (up to unitary equivalence) decomposition of non-denereate (multiplicity-free in this case) representations of separable GCR $C^*$-algebras (see e.g. Dixmier, 8.6.5) into direct integral of irreducible ones.
Is there such decomposition in the non-separable GCR case (as hinted here)? Most of the references I found focus on a separable case. Perhaps there are some weaker generalizations for some special (non-separable) cases?