Carmack owns the IP for Doom?
The IP debate gets old, especially among forum lawyers. Fact is that IP protection gives owners the ability to defend their products and brand. It doesn't mandate auto-kill for all such projects.
The IP argument is not an excuse to avoid doing things or 'give up' before the first steps. IP rights can be scary especially with horror stories that do happen from time to time. But in the real world, people and organization
TALK,
DISCUSS, and
NEGOTIATE issues rather than just sending in the nukes. I'd consider a C&D as simply an open invitation for discussion.
That being said, This is a
GOOD idea. Do it.