Havok 4 (now belongs to Intel), the recent version of the physics engine Second Life uses, is going into beta test. This is something many people have been waiting for one or two years.
This is first going to be a change under the hood; Lindenlab expects a more reliable SL experience out of it. So you should not expect big changes in the beginning.
Later this could lead perhaps to better prims per vehicle, since many ppl awaited this feature for long. We are going to see.