I think its a good idea that the gametypes are trimmed down..what hal said is true, it wouldn't be too difficult to make mods of BR or DOM (vCTF has never been an official gametype, so Epic aren't ditching it...they never picked it up in the first place).
When you look at
Csports stats (no bots) they show the most popular gametypes are:
ONS 82 000 players in the last month
DM 64 000 players
CTF 55 000 players
-then there is a massive drop before you get to Assault, so it makes sense to concentrate on these gametypes as these are what are keeping the game alive. Besides, with just 4 gametypes to map for you'd hope that the quality across all gametypes will be top notch.
Also, for the people who don't like ONS, it's worth noting that it since UT2k4 came out it has consistantly been the most popular gametype online...Epic would be foolish to drop something that most people like so much.
Now, I love DM and TDM, but I play ONS most of all, and my clan is an ONS clan so perhaps I'm biased, but I don't think you can say that DM maps suffered in UT2k4 because of ONS, the game came with A LOT of quality DM maps, and since then the vast majority of community maps seem to be DM. Most map packs (the CBPs and the recent UCMP) always have more DM or CTF maps than ONS, and while Epic did release the ECE which was purely ONS, there have been some incredibly high quality map packs that have focused on CTF and DM (the Flag Packs and the 1-on-1 pack for example).
So with the more concentrated focus on fewer gametypes, I don't think there is any danger that Epic will not give due care and attention to the core gameplay mechanics and maps of the staple gametypes; DM, CTF and now ONS.
Still, this Conquest mode sounds really interesting. The mention of "Assault like objectives" is perhaps why they decided to drop Assault ( a gametpye that I want to like, but find to spammy...a more wide open approach to objectives, like ONS, might make it more interesting to me).
Also, there's a mention in there of more "face to face combat"..which if it is done well (perhaps objectives that can't be reached with vehicles) should make it better for people who went off Onslaught because there is not enough DM style fragging in it.
One worry about Conquest is how long games will last on maps this size. I've played games of onslaught between 2 well matched teams that have gone on for over an hour..and that's just one round.
Still, from the videos that we've seen of the U3 engine, this looks as though its going to be awesome...and I'm already thinking about getting myself a new computer to run it on.
Also, agree with Selerox, no stupid UT2k6 name or whatever, it has to be UT3...there really can't be any other title