A good community is very important for an indie game. We want to achieve that using modding. But UE4 would make modding very complicated, seeing that the modder must buy a subscription if he wants to make a mod. Or we have to make some sort of modding tool, which also isn’t easy. But UDK will allow modders to just download the Engine and make a mod. Okay, maybe not that simple. But simpler than UE4. UDK also is free.
Which brings me up to another question: Will UDK be always updated, so even when we use it we can provide the best user experience? Or if we want all the amazing looks we need to have UE4?
I don’t think you necessarily need to have them buy a subscription. If you want them to create assets using the Unreal editor, then sure they need one. However if you create your own map editor/scenario editor within your game, where they can create their maps/mods using your own ingame editor, they just need to have your game in order to add content to it. I believe that wouldn’t violate the ToS/EULA at all and would be a way around them paying the fee for Unreal. However, you’re obviously looking at a ton of work making your own in game editor, but that’s why you pay for Unreal - you either make that part, or you let your modders pay too.
You could make your own tool, which could end up being a lot of work, but you can’t give away any of the UE4 source code or tools.
By the way, UDK is not free, if you are selling a game then you still have to pay a fee, it’s free to use but not free to sell a game.
You can still do really nice looking things with UDK, but there’s less platform options, and as far as updates go, it’s going to be very limited if anything.