Small Screen Rendering mode
How does this differ from the desktop SSR mode, which has been available for the best part of a decade? Or is this just a marketing gimmick to boost awareness of the feature amongst web designers? Perhaps some people think they need to be using a special tool to test their mobile pages and don't have faith in SSR mode on a desktop version?
I can't see this new version being any different because surely it's still subject to the same limitations. For example, different phones may have different fonts, and Mobile Opera being simulated on a desktop is probably going to use your desktop fonts or at best get bundled with one font of its own.
And as for widgets, you need to specify a width and height for them, so if you want to develop them on a desktop, surely you just set their sizes to those of phones?
I think Opera's 'Widget platform' thingy is already in Opera 10.5. Widgets can now be installed and removed from the Windows control panel rather than the Widgets panel of previous versions, thus presenting them to the user as proper applications rather than specialist HTML5 web pages.