In terms of general creative freedom, players are definitely very limited with what they can use. The developer understands the importance of mods to a lot of players, but I think they didn't really have mods in mind as much compared to ensuring the singleplayer and multiplayer would be a worthy successor to the originals.

I wouldn't be surprised if the next game (it's safe to say that given the success of DOOM 2016 that there will be another) had additional features for modders to use, thus giving them more freedom.

I'm sure most major fans of mods will for now just go back to the originals.