Yeah you can do almost everything since you have access to the c++ code. But for an RTS for exemple what you want is users to be able to make custom maps at the very least. Some games will extend that to custom units/models, weapons and so on. I don’t think the epic way is viable option for kind of case. Game devs could always do custom tools but one of the greatest thing with UE is the editor so I don’t see the point of doing that and I don’t know how the engine will do with dynamic generated content in a map compared with a map entirely done in the editor.
Things might change in a near futur, with UE4 released with the whole source code for almost free everyone else will have to make a move if they want to keep the indie market and Epic just proved to everyone that they do not only care about big companies. Seriously I don’t think anyone saw that coming and Epic will still adjust things as it’s go like they they did with royalties in UDK.
The first thing is always to prove that you are serious, start doing your game and show it to them and you’ll probably able to speak with them and maybe make a custom deal. Just don’t say I have a crazy idea for a game but I need to ship the game with the editor while showing nothing, no one will ever listen to that.