One bright spot in this post-Microsoft client application future will be the elimination of the traditional software distribution model. No longer will IT shops have to track and manage a huge library of installed, stand-alone applications. With everything streaming from the cloud, the days of corrupted MSI packages and nasty DLL-hell scenarios will become a distant memory. The flip side of this equation is that the capability of working "offline" will also become a thing of the past. Your entire application infrastructure will be wholly dependent on uninterrupted connectivity to the cloud, making the Internet itself your new single point of failure.
Bottom line: Expect increased support and training costs as users struggle to master common functions across disparate applications. You may also want to update your disaster planning to include the pre-apocalyptic nightmare scenario where a backhoe operator takes out your now cloud-dependent IT infrastructure with an errant swing of his mighty shovel.
Developer tools: Bloody purges and API turf wars will shape the new standards
As with client applications, the developer tools landscape will be fundamentally altered by the inevitable decline of the Win32 API. Programmers will face a plethora of new and potentially critical design decisions, including how to create a workable UI in a world where the old Windows rules no longer apply. The potential for freedom of expression and true innovation will need to be balanced against the reality of having to test early and often to ensure that your latest idea for a revolutionary new interface paradigm still plays in Peoria.
One of your first challenges will be achieving the level of UI richness that you became accustomed to in the pre-decline Windows era. AJAX, CSS, and HTML will have come a long way since the days when YouTube and Facebook were household names. However, these and similar Web technologies will still be restricted by the limitations of the underlying document model. And with the world's regulatory agencies eventually banning Adobe Flash (and similar RIA solutions) for the good of the Internet -- which was collapsing under the stress of a gazillion animated Viagra ads -- you may find your options for creating a compelling UI to be limited to strategically placed GIF images, DIV tags, and some clever use of HTML table borders and shading.
Another consideration will be how to integrate any newly designed application with the broader Web. Popular back-end data exchange APIs will abound, each with its own camp of fervent supporters, so you'll need to choose wisely. The last thing you want is for your world-changing killer application to be relegated to obscurity due to a lack of interoperability with the rest of the cloud.
On the plus side, the demise of Windows means you'll never again have to worry if the user has the correct version of a critical DLL or library installed so that they can run your application. Likewise, the chicken-and-egg debate over the .Net framework will be finally resolved (in favor of the chicken). However, the days of the "standardized" UI will be over, making the job of creating applications that work consistently, and which interact with both the user and other applications in a predictable manner, that much more challenging.
Bottom line: Expect much confusion as the newly cloud-centric world reorders itself through a series of bloody purges and API turf wars. Navigating this minefield of fleeting pseudo standards and technology dead ends will help to separate the wheat from the developer chaff. Only the strong will survive.
Hardware ecosystem: Chaos until a new overlord rises
Perhaps the most powerful ripples of the post-Windows shockwave will be felt in the PC hardware and peripherals marketplace. The lack of a dominant OS target will cause the once homogenized device driver landscape to fracture, with vendors chasing after the popular platforms du jour while neglecting their legacy installed base. Plug and play will be replaced by "plug and pray" as frustrated customers struggle to match devices to their respective OS choices, while wondering if they'll regret their selections once the next tide of disruptive development rolls in.