Limit multiplicities in SL(2,R)^r+ SL(2,C)^s

Let G be a semisimple Lie group with unitary dual ^G, and L a co-finite lattice in G. L can be used to define a measure m_L on ^G in a natural way. A natural question is, whether m_L tends to the Plancherel measure on ^G if L varies over a family of co-finite lattices with vol(L\G)->infinity. This has been proven to be true in many situations in which the lattices are either commensurable with each other, uniform in G, or G=SL(2,R) or SL(2,C). In my talk I want to discuss this problem for the natural family of lattices SL(O_F) in G = SL(2,R)^r+SL(2,C)^s when F runs over all number fields with fixed archimedean signature (r,s) and O_F is the ring of integers in F.