The plans for Scion include a heavily redesigned version of the xA that dumps the current doorstop physique for a shape yet to be released. The xB will remain a toaster, as the box form is something that, according to Autoweek's contacts, will endure throughout the models lifespan. Expect to see revisions to the tC towards the end of the decade with styling cues coming from the New York Auto Show's Fuse concept. One additional model will be added, most likely carrying the name xD (they've already applied for the trademark), which will be something of a Matrix replacement, not a stretched version of the xB as had been previously thought.
Mazda's got their own thing going on and we can only hope that the upcoming models/redesigns carry more of their patented zoom-squared DNA.
At the forefront, in our minds at least, is the Kabura concept that debuted in Detroit. If Mazda decides to bring over the MX-5 based coupe, expect to wait until 2009 at the earliest (insert weeping and sniffing noises here). They could've pacified us in the meantime by bringing over the Mazda2 subcompact that's currently available in Europe, but after researching what the U.S. market (supposedly) would want, they deemed the project terminal and have since called off any plans for importation. A design study was performed on the RX-8 and nothing is planned beyond a revamping for the 2010 model year.
The Mazda3 is due for a redesign, which should literally take shape in 2009, with some small revisions being made in the meantime. The Mazda6 will down some Enzyte and grow in all dimensions in order to better compete with the Accord and Camry, with parts being shared with its stable mate the Ford Fusion.
The MPV and Tribute will be put out of their misery by 2007, with the latter coming back as the CX-5 in 2008. A CX-9 is in development to fill the minivan sized whole left by the MPV, which should find its way onto roads late next year.
You can get all the details, in their entirety, here and here.