Frankly, I don't think many people here have much knowledge on the Dragon Quest series so that's why you guys hare 'pessimistic' about it. As someone who has been following it for years, its easy to guage how it'll do. No matter what system the game goes to, the Japanese fanbase will follow. And the Japanese fanbase likes the Wii the most right now, eventhough Wii sales have been lukewarm. You know why that is? Because there's lukewarm support from third parties.
You've seen what happens, even in Japan, when a good game like New Super Mario Bros comes out over there. They go through the same ridiculous numbers we do in the west, with thousands of people buying the game a week (up to nearly 1/3 the Japanese Wii userbase already owning the game). What makes you think Dragon Quest X won't sell similarly? Its easily a game Japan wants, on a popular (and cheap) console and being hyped for multiple years.
It'll sell just fine. At least near the numbers of DQVIII (3.6m) if not more. The real issue is in the west and whether or not SquareEnix is going to actually try to advertise DQIX enough to make it popular, thereby opening a hype window for DQX so it can sell in the future. There's 4 unreleased Dragon Quest titles coming to the west (Dragon Quest IV DS, Dragon Quest IX, Dragon Quest Monsters: Joker 2 and Dragon Quest X) and SquareEnix once again has the chance to start a marketing push to make those games sell better. Or they can do nothing as they have been and watch them fail miserably like the last few entries. If SquareEnix would put even 1/4 the marketing into the DQ games as they do their Final Fantasy titles, they could probably work up to making a Million on each Dragon Quest title in the west. As it stands now, they're looking at barely making 10,000 in sales on DQIX.