The photo released for the new page shows a left-hand column which now links to popular Yahoo services shows a column allowing for user-picked, customizable applications, and the site also boasts the ability to check other email accounts such as G-mail and AOL. While the site itself is the first redesign in two years, as I've written recently in regards to Facebook, it is incredibly important not to upset your viewer base by radically uprooting their perception of your site. Facebook has been experiencing a mild backlash for their new roll out, and it may take some time and effort before that unrest goes away.
The future of web development for Yahoo is similar to many other major sites (like Google and Facebook) that allow third party developers to design applications for users. The company intends to continually improve their site and inform their user about both their activity and that of others on the net.
The last redesign by the web mega-giant was rolled out over 6 months. This new design will probably take a similar amount of time to fully implement, although the company doesn't have any specific dates set in stone.