Todd Hollenshead has posted another update to his .plan file, this time providing some details left out from the original announcement:
Mac and Linux: Unfortunately I don't have dates for either of these. However, Linux binaries will be available very soon after the PC game hits store shelves. There are no plans for boxed Linux games. More remains to be done for the OSX version of DOOM 3 and that will take some time.
Demo: our priority was finishing the game first and now we are turning our attention to the demo. I don't have any information to share regarding any specific content, but I don't believe that we have ever disappointed in that regard in the past.
There's more, so be sure to read the whole thing.