It would be tricky: constraint solving is a single-threaded algorithm, so the best option might be to run the broad-phase, and then break the scene down into islands of disconnected bodies for parallel constraint solving.

The problems are that: 1) There may not be enough islands to make full use of the available threads. 2) For many frames there might be a single island which is particularly expensive to solve, so the benefit from parallelisation is reduced.

The broad-phase itself might benefit significantly from parallelisation though.