First of all, it's good to see an "old" player making a return. Welcome back, Aden-player :)
I remember the Aloisio character, and the discussion you started back then about newbies writing together. I had only just joined the game, and was interested in the discussion, although I was (and still am) primarily a gamer not a writer, so I never got involved with the thread. If I recall correctly, you had a story taking place in the Quarantine Zone/Corvidae Flats? I think that you had a lot of interest in your idea, and that quite a few characters joined the thread :)
That's why I think that this is a great idea!
Build it, and they will come!
I doubt that many older or more experienced players will get annoyed or feel excluded by a thread created to encourage new players to write together. Instead, I imagine that they would actually encourage such a venture because it may help new players take their first steps into the world of RP, and help to keep them here - held captive in thread chains and writing handcuffs! Jumping into your first thread in a new game can be daunting. I can see how new players such as Kendal, who has posted here, may have no difficulty in getting involved because Kendal-player is clearly an excellent writer (loving your work so far!), but not every new player is going to be that skilled. Let's face it, the majority of threads here are incredibly exclusive. They are usually started by two or three players who want to write together. In that respect, a thread exclusively for new players is no different to most threads here. As for limiting the numbers to around 10 potentially causing more feeling of exclusion to arise, I really don't see that as a problem at all. I would love, LOVE to read a thread with 10 characters involved, but I don't remember many such threads, so please don't worry about that :)
I would definitely go ahead with your plan, but probably create the thread using the [Open] option, as the earlier posters have mentioned. Be warned, though: generally, open threads are still pretty hit and miss. Almost half seem to die before a reply has been made, or after just one response, while nearly half seem to have 6 or 7 replies in quick succession, and appear to be about as open as a clam's arse in a tsunami. However, the ones that survive are always a good read :) An "open" thread that has had a bit of discussion in the forums before it is posted, may well be the way forward.
A month or two back, there were only about 100 active. unique players. There are, apparently, over 130 at the moment, so the opportunities for more RP are rising!
Good luck with your suggestion :)