What to Expect from Transiting Multiplanet Systems
  So far radial velocity (RV) measurements have discovered ~25 stars to host multiple planets. The statistics imply that many of the known hosts of transiting planets should have additional planets, yet none have been solidly detected. They will be soon, via complementary search methods of RV, transit-time variations (TTV) of the known planet, and transits of the additional planet. When they are found, what can transit measurements add to studies of multiplanet dynamical evolution? First, mutual inclinations become measurable, for comparison to the solar system's disk-like configuration. Such measurements will give important constraints to planet-planet scattering models, just as the RV measurements of eccentricity have done. Second, the Rossiter-McLaughlin effect measures stellar obliquity, which can be modified by two-planet dynamics with a tidally evolving inner planet. Third, TTV is exquisitely sensitive to planets in mean motion resonance. Two planets differentially migrating in the disk can establish such resonances, and tidal evolution of the planets can break them, so the configuration and frequency of these resonances as a function of planetary parameters will constrain these processes. 
Daniel C. Fabrycky