In a few months they have to freeze the development and stabilize the code for release. There is no time for major changes, expect only small tweaks. The final version will be similar to this preview.
Usually that would be the case. With Windows 8, the first public release was the Windows Developer Preview, they dished out an SDK, and tried to get developers making apps. Then came the Windows Consumer Preview, that was when the UI was mostly finished. After that was the Windows Release Preview.
Microsoft is ready to listen to feedback this time, and it shows throughout all their actions so far. Windows 10 is built to update from build to build in one click. It also records telemetry data in near real-time, and we've seen it also ask you for your feedback when doing things in Windows.
They aren't dishing out an SDK to developers, this is more or less the refinement of where Windows 8 was going. They will first and foremost listen to Windows customers about what is wrong, and what they can do to fix it. Once they nail down the functionality and usability perspective of Windows 10, the consumer preview will come out with a Modern 2.0 look, not the developer preview like jmshub said. They showed us the roadmap and developers are last this time, not first.
Also personally, I don't see a major problem with Continuum, I see how it could be improved, and I see where you're coming from. I like the touch gestures Windows 8 uses on tablets, and the taskbar shouldn't be visible with full-screen apps. But these are small flaws that could easily be reported during feedback of Continuum.
Continuum could be very useful on tablets like the Surface Pro 3. But tablets like the Surface 2 I think the current start screen fits it the best. A scaled-up Windows Phone start screen might look like a crippled UI on the Surface 2, but a small Lumia tablet the size of the cancelled Surface Mini, I think it would be perfect for that. At the same time, it all has to mesh together, nothing can look too different, just laid out differently. I think it will all come down to what feedback from customers shows, if I'm unhappy with my Surface 2 and others are too, they'll adjust the layout and tweak it more in the next build.