Yeah you need to change the name of the thread or put an explanation right up front in the OP that we're talking about TDM's engine and not Thief's Dark Engine, since it's very confusing.
It's true that our engine is quite different from idtech4 at this point. If you look at the sourcecode for both, I mean just the folder of files, it's blatantly obvious just by sight. So it deserves its own name. But I think in practice people would just call it the TDM Engine. Most of discussion about it is in the Developer's forum here though, since it's still in development from version to version.
What it looks like you're talking about in the OP--putting up a public page on the engine--is really for branch projects separate from the team, for fans that just want to play around with it. I mean, that's what I think its value would be, since we already have people working on the engine for the next version internally. Anyway, I think that would be a valuable thing, because we all have the open-source ethos around here of share-alike. Our engine is a good engine, and it'd be a great base for all sorts of indie games, much better than most other open source engines you could start with (to say nothing of smaller possible branch projects, like "multiplayer TDM" or "TDM+Mirror's Edge 2 Moves", etc, a fan could do just for fun.) But for it to have that role, it needs some primers to get fans out there to know how the code works and how to experiment with it.
Edit: That said, the code is maaasive. Such a project would be a fantastic undertaking. And I don't know how useful a basic explanation would be anyway. Nothing really beats just opening up the code & reading it oneself, and experimenting with it locally to see what happens, and then maybe asking one of our coders any questions. Something to be said for the good old fashioned way.
Edit2: Also like Serpentine is saying, you have to distinguish projects you want the team to do for TDM in future versions versus projects you want to do yourself locally, just for yourself, or other fans doing it for themselves. Projects for yourself you are free to do at your leisure. And if it turns out really well, you might show it to some people & make a good case for inclusion in the mod if it really is special. But for doing things for the mod, it's a much bigger deal, because then you have to get the team involved & there has to be a lot of debate and back & forth discussion and bug fixing and you have to know when to push and when to compromise... In my experience, when you're starting off learning the code, the best thing to do is just play around with it locally for yourself and make some changes that make you happy, and once you get used to how things work, and also how the mod works, you can think about what's worth bringing to the attention of the team.
Edit3: And incidentally, there are established things around already... There's a page specifically on things we might want to add to the engine now that it's open source. http://wiki.thedarkm...ch4_Open_Source
Adding to that wiki page, making a thread on the forums with a request, & adding feature requests to the bug tracker (probably after vetting it in a post first) are the first places you'd probably start with requests for what we might do with the engine.