I just don't get waiting for the Japanese knowing that even if Yamaha or Honda did release a 450 dual sport the motor would be "retuned for midrange", the suspension would be a generation back and it would gain at least 50 pounds over the competition model. The best the Japanese have managed to do is the WR250R and it literally weighs as much as my 640 with maybe half the power.
Meanwhile KTM builds an EXC 450 that is fast, handles great, has great brakes, is light weight, extremely rugged, adaptable and sitting at the dealer now. Don't want to pay KTM prices then buy used. I did. Husky also makes one that is pretty damned good and ready now. And having ridden with dozens of EXC's, I know for a fact that this idea of them being somehow fragile is complete nonsense.
As for maintenance remember that an EXC maintenance schedule assumes race duty. The guys I know riding them as dual sports aren't doing anymore than I ever did to my Japanese dual sport bikes. As for oil capacity, my XT350 only held 3/4 of a quart and it saw 25k miles of very hard abuse. Keep it fresh, use good oil and it doesn't matter. I change the oil in dual sports a lot anyway because I ride mostly offroad.
So keep on waiting for the Japanese if you want. I was a 23 year Yamaha dual sport rider and I certainly did for many years. But when they finally released a new dual sport it was a 300 pound 250. And I don't want ANY four stroke 250 much less one that heavy. Then I rode a couple of KTM's and the proverbial light bulb went off. I am not the least bit sorry to have tasted Koolaid. In fact, now I want more.
525EXC, 640 Enduro, XT200