The big problem with AIP with stepping behind it is that beyond a certain level (whatever makes MK3 planets to core worlds) it is essentially game over if by that point you haven't killed all the shields and at least 1 homeworld + survived the response. Especially since this applies to ALL worlds, which if you hit the first "stepping" of AIP, can lead to the fastest game over ever, as you could face core ships in actual regular attack waves before you even have more than 1 MK3 ship unlocked.
####
Btw, I hope we get some deeper scripting ability than just XML for modding.. the game begs for LUA integration with hashing applied so that mods can work together in MP.. don't hardcode your campaign core logic if at all possible and allow us to add dialog boxes and if/else triggers + some more logic based scripting (count ships in planet X, do Y if number is Z, display popup box, modal dialog with image AAA and then play sound file whatever*)... it was already what killed modding in many previous Unity games not just by Arcen. This is especially important as the Unity engine is a huge detriment to modding if you don't expose core API elements. (ie, allow us to sideload DLL's with decent documentation) ala KSP.
If you do not plan on adding scripting beyond XML, then at least consider allowing sideloading of DLL's that interact with core game logic and can extend various things, like a script extender (which in turn allowed sideloading DLL's into Skyrim. It would require good documentation and a build guide, but it would also allow for vastly better and more awesome mods, especially if the game gains any mass market traction
Ps.: Though it obviously requires you to add code based triggers for advanced scripting as the one I exemplified above ;P