Ok... heres the fun part. Explorer will be based around a small bootstrap loader which will start up the library code. All the functionality of Explorer, it's gfx routines and so on will be implemented via libraries. This means that it will be easy to produce different versions of the code. As things stand at the moment I am considering writing versions of the libraries for AGA and RTG. (as a combined AGA/RTG lib is too slow on AGA and cumbersome on RTG) However, because of the structure of the libraries it should be possible for 3rd parties to develop ECS routines.
The other graphics engines will render onto a normal intuition screen (minus titlebar and gadget of course) for maximum OS compatability.
Input devices are interpreted by control modules which watch the ports and produce signals which the user can configure in the game controls editors. Each ships will have it's own actions and movement definitions which can be triggered by user defined keys.
All the systems controls can be defined and each ship's controls can be separately configured (optional). Many ships have preset manoeuvres which will be triggered via a single keypress (like a flip roll).