Whilst it's nice to think in separate concepts such as 'physics' and 'rendering', in reality all these things are tightly coupled together in code. For example collisions inform physics which informs collisions which informs animations etc. Also with memory being so scarce in AAA games you have to evaluate the cost of using separate threads for different actions, which leads to problems of resource sharing, deadlocks, syncing of update/render loops etc.
Bungie did a talk on their multi threaded renderer for Destiny. Google it if you want to see how complex the design can get, and how it affects the whole game process.