The book after tCatC is very likely to be Hermetic Projects. (It isn't back from the printer yet. Something could still go horribly wrong.) Since tCatC is going to be out in November, I suspect it won't be a December release, but release scheduling isn't my department.
I love how we are all looking eagerly forward to the next book when we do not have the previous one yet :mrgreen:
Xavi
Jeez now you're just embarrassing us.
Well, I am not in a different group 
I would like to know the full timeline of books and their theme for the next 5 years :mrgreen: heheheh
passes Christian a guide to semaphore
This is true, but it's balanced out by the Black Monks of Glastonbury which is extra heavy (although not overwhelmingly so) on myth, legend, and the realms. When those two are viewed together I think they stand up well even when compared to the fifth edition books.
I suspect if Atlas wanted to release an updated version the content from these two books would be fairly easy to update (many sections could be brought over with only minor tweaking). But then this is a rather good argument to make this the last book to update - it's already enough enough for gamers to do it themselves. I could be wrong but I believe this was the last 4th edition tribunal book, which means it was likely to be the last updated anyway.
Oooh, that looks cool...
...says the author of 2 locations ;D
Not that I would contradict him 
That indeed DOES look cool 
Will it be only hermetic features descriptions (and rules and numbers backing them) or will it also contain adventuring and plotting parts?
The emphasis is on the Hermetic stuff for player characters to do, but there are lots of story seeds for things that might happen while they are doing it. The idea is for these projects to be player-driven rather than storyguide-driven, however.
Which is often how Ars Magica works best! 