@k_joseph, for each type of result, there is both a result display (in the list on the left) and a detail pane display (on the right). Are you using an interface for both of these? Ideally, each “out of the box” result type you support should be implemented through those interface, so they can serve as examples to module owners who want to add additional result types.
Try to avoid horizontal scrollbars at all costs. 
Some features that I don’t know if you’ve yet addressed:
- Keyboard navigation through results
- Handling large numbers of results (paging vs. infinite scroll vs. a little of both). Infinite scrolling is convenient, but if placeholders are not used, then the scroll thumb does not imply the full number of results and, depending on how many results are fetched at a time, it can be laborious to get to the end of the list of results.
- Ensure that rendering never blocks the user.