The UE4 Plugin that we are currently developing will be released with both a free (basic functionality) and paid (advanced functionality) component to the plugin.
Also we will allow a team to use both the basic and advanced versions of the plugin side-by-side without requiring a team to purchase an advanced license for each individual user on your team when say only 2 out of 6 of your team require that functionality.
We believe by doing this we can get our plugin into as many developers hands as possible and only those which need the advanced functionality can individually update their license from the free (basic) to the paid (advanced) version at their own expense.
I believe you underestimate the complexity of a 3D graphics engine compared to that of a 2D document editor 