We don't like to discuss details, which are not already implemented. So, don't expect to hear many details about the new engine until its development is advanced enough.
In general, the new engine will be a completely new platform from the ground up, including the graphics engine, terrain, database structure, etc. However, the code written specifically for Black Shark was designed with portability in mind, so most of the relevant parts could be "moved" to the new engine with minimal recoding effort required. For example, the new mission editor is already prepared for the new engine.
As mentioned before, DCS is currently running on the modified TFCSE engine and until the new engine is ready, this will continue to be the case. We can't estimate when this may happen, because developing the new engine is only one of many development tracks for ED and sometimes progress is faster than others, depending on the availability of resources and the need to ditribute programmers to other projects/contracts.