This idea has been discussed on IRC a bit as well, and it sounds great to me. I agree that a full megawad is overambitious by far, but a smaller doom 1 style single mini-episode is more viable.
I used to do some mapping a long, long time ago, and the tools and tech have come a long way since then. I’m definitely down to attempt to make a map for this.
My personal favorite style of map are the episode 1 style techbases, so I’ll probably do one of those. If there are more volunteers with different preferred styles we could probably arrange them into a loose arc.