I am in the midst of creating a mod (so far for personal recreation) which combines several parts of all the official classic doom into one.
Ultimate, Sigil, Doom 2, Final Doom, Master Levels, NRFTL, as well as console-exclusive content and Romero's bonus e1 maps.
(This project is targeted for GZDoom and aims to do more than any other combination project I know of)
If I ensure that an IWAD is still required, will there be any problems if I were to release it?